6 February 3, 1865 s. 4.)
As wild plants are so rarely liable to bud-variation, whilst highly cultivated plants long propagated by artificial means have yielded many varieties by this form of reproduction, we are led through a series such as the following,--namely, all the eyes in the same tuber of the potato varying in the same manner,--all the fruit on a purple plum-tree suddenly becoming yellow,--all the fruit on a double-flowered almond suddenly becoming peach like,--all the buds on grafted trees being in a very slight degree affected by the stock on which they have been worked,--all the flowers on a transplanted heartsease changing for a time in colour, size, and shape,--we are led by such a series to look at every case of bud- variation as the direct result of the conditions of life to which the plant has been exposed. On the other hand, plants of the same variety may be cultivated in two adjoining beds, apparently under exactly the same conditions, and those in the one bed, as Carriere insists (11/158.
"Production des Varietes" pages 58, 70.) will produce many bud-variations, and those in the other not a single one. Again, if we look to such cases as that of a peach-tree which, after having been cultivated by tens of thousands during many years in many countries, and after having annually produced millions of buds, all of which have apparently been exposed to precisely the same conditions, yet at last suddenly produces a single bud with its whole character greatly transformed, we are driven to the conclusion that the transformation stands in no DIRECT relation to the conditions of life.
We have seen that varieties produced from seeds and from buds resemble each other so closely in general appearance that they cannot be distinguished.
Just as certain species and groups of species, when propagated by seed, are more variable than other species or genera, so it is in the case of certain bud-varieties. Thus, the Queen of England Chrysanthemum has produced by this latter process no less than six, and Rollisson"s Unique Pelargonium four distinct varieties; moss-roses have also produced several other moss- roses. The Rosaceae have varied by buds more than any other group of plants; but this may be in large part due to so many members having been long cultivated; but within this same group, the peach has often varied by buds, whilst the apple and pear, both grafted trees extensively cultivated, have afforded, as far as I can ascertain, extremely few instances of bud- variation.
The law of a.n.a.logous variation holds good with varieties produced by buds, as with those produced from seed: more than one kind of rose has sported into a moss-rose; more than one kind of camellia has a.s.sumed an hexagonal form; and at least seven or eight varieties of the peach have produced nectarines.
The laws of inheritance seem to be nearly the same with seminal and bud- varieties. We know how commonly reversion comes into play with both, and it may affect the whole, or only segments of a leaf, flower, or fruit. When the tendency to reversion affects many buds on the same tree, it becomes covered with different kinds of leaves, flowers, or fruit; but there is reason to believe that such fluctuating varieties have generally arisen from seed. It is well known that, out of a number of seedling varieties, some transmit their character much more truly by seed than others; so with bud-varieties, some retain their character by successive buds more truly than others; of which instances have been given with two kinds of variegated Euonymus and with certain kinds of tulips and pelargoniums.
Notwithstanding the sudden production of bud-varieties, the characters thus acquired are sometimes capable of transmission by seminal reproduction: Mr.
Rivers has found that moss-roses generally reproduce themselves by seed; and the mossy character has been transferred by crossing from one species of rose to another. The Boston nectarine, which appeared as a bud- variation, produced by seed a closely allied nectarine. On the other hand, seedlings from some bud-variations have proved variable to an extreme degree. (11/159. Carriere "Production des Varietes" page 39.) We have also heard, on the authority of Mr. Salter, that seeds taken from a branch with leaves variegated through bud-variation, transmit this character very feebly; whilst many plants, which were variegated as seedlings, transmit variegation to a large proportion of their progeny.
Although I have been able to collect a good many cases of bud-variation, as shown in the previous lists, and might probably, by searching foreign horticultural works, have collected very many more cases, yet their total number is as nothing in comparison with that of seminal varieties. With seedlings raised from the more variable cultivated plants, the variations are almost infinitely numerous, but their differences are generally slight: only at long intervals of time a strongly marked modification appears. On the other hand, it is a singular and inexplicable fact that, when plants vary by buds, the variations, though they occur with comparative rarity, are often, or even generally, strongly p.r.o.nounced. It struck me that this might perhaps be a delusion, and that slight changes often occurred in buds, but were overlooked or not recorded from being of no value.
Accordingly, I applied to two great authorities on this subject, namely, to Mr. Rivers with respect to fruit-trees, and to Mr. Salter with respect to flowers. Mr. Rivers is doubtful, but does not remember having noticed very slight variations in fruit-buds. Mr. Salter informs me that with flowers such do occur, but, if propagated, they generally lose their new character in the following year; yet he concurs with me that bud-variations usually at once a.s.sume a decided and permanent character. We can hardly doubt that this is the rule, when we reflect on such cases as that of the peach, which has been so carefully observed, and of which such trifling seminal varieties have been propagated, yet this tree has repeatedly produced by bud-variation nectarines, and only twice (as far as I can learn) any other variety, namely, the Early and Late Grosse Mignonne peaches; and these differ from the parent-tree in hardly any character except the period of maturity.
To my surprise, I hear from Mr. Salter that he brings the principle of selection to bear on variegated plants propagated by buds, and has thus greatly improved and fixed several varieties. He informs me that at first a branch often produces variegated leaves on one side alone, and that the leaves are marked only with an irregular edging or with a few lines of white and yellow. To improve and fix such varieties, he finds it necessary to encourage the buds at the bases of the most distinctly marked leaves, and to propagate from them alone. By following with perseverance this plan during three or four successive seasons, a distinct and fixed variety can generally be secured.
Finally, the facts given in this chapter prove in how close and remarkable a manner the germ of a fertilised seed and the small cellular ma.s.s forming a bud, resemble each other in all their functions--in their power of inheritance with occasional reversion,--and in their capacity for variation of the same general nature, in obedience to the same laws. This resemblance, or rather ident.i.ty of character, is shown in the most striking manner by the fact that the cellular tissue of one species or variety, when budded or grafted on another, may give rise to a bud having an intermediate character. We have seen that variability does not depend on s.e.xual generation, though much more frequently its concomitant than of bud reproduction. We have seen that bud-variability is not solely dependent on reversion or atavism to long-lost characters, or to those formerly acquired from a cross, but appears often to be spontaneous. But when we ask ourselves what is the cause of any particular bud-variation, we are lost in doubt, being driven in some cases to look to the direct action of the external conditions of life as sufficient, and in other cases to feel a profound conviction that these have played a quite subordinate part, of not more importance than the nature of the spark which ignites a ma.s.s of combustible matter.
CHAPTER 1.XII.
INHERITANCE.
WONDERFUL NATURE OF INHERITANCE.
PEDIGREES OF OUR DOMESTICATED ANIMALS.
INHERITANCE NOT DUE TO CHANCE.
TRIFLING CHARACTERS INHERITED.
DISEASES INHERITED.
PECULIARITIES IN THE EYE INHERITED.
DISEASES IN THE HORSE.
LONGEVITY AND VIGOUR.
ASYMMETRICAL DEVIATIONS OF STRUCTURE.
POLYDACTYLISM AND REGROWTH OF SUPERNUMERARY DIGITS AFTER AMPUTATION.
CASES OF SEVERAL CHILDREN SIMILARLY AFFECTED FROM NON-AFFECTED PARENTS.
WEAK AND FLUCTUATING INHERITANCE: IN WEEPING TREES, IN DWARFNESS, COLOUR OF FRUIT AND FLOWERS.
COLOUR OF HORSES.
NON-INHERITANCE IN CERTAIN CASES.
INHERITANCE OF STRUCTURE AND HABITS OVERBORNE BY HOSTILE CONDITIONS OF LIFE, BY INCESSANTLY RECURRING VARIABILITY, AND BY REVERSION.
CONCLUSION.
The subject of inheritance is an immense one, and has been treated by many authors. One work alone, "De l"Heredite Naturelle" by Dr. Prosper Lucas, runs to the length of 1562 pages. We must confine ourselves to certain points which have an important bearing on the general subject of variation, both with domestic and natural productions. It is obvious that a variation which is not inherited throws no light on the derivation of species, nor is of any service to man, except in the case of perennial plants, which can be propagated by buds.
If animals and plants had never been domesticated, and wild ones alone had been observed, we should probably never have heard the saying, that "like begets like." The proposition would have been as self-evident as that all the buds on the same tree are alike, though neither proposition is strictly true. For, as has often been remarked, probably no two individuals are identically the same. All wild animals recognise each other, which shows that there is some difference between them; and when the eye is well practised, the shepherd knows each sheep, and man can distinguish a fellow- man out of millions on millions of other men. Some authors have gone so far as to maintain that the production of slight differences is as much a necessary function of the powers of generation, as the production of offspring like their parents. This view, as we shall see in a future chapter, is not theoretically probable, though practically it holds good.
The saying that "like begets like" has, in fact, arisen from the perfect confidence felt by breeders, that a superior or inferior animal will generally reproduce its kind; but this very superiority or inferiority shows that the individual in question has departed slightly from its type.
The whole subject of inheritance is wonderful. When a new character arises, whatever its nature may be, it generally tends to be inherited, at least in a temporary and sometimes in a most persistent manner. What can be more wonderful than that some trifling peculiarity, not primordially attached to the species, should be transmitted through the male or female s.e.xual cells, which are so minute as not to be visible to the naked eye, and afterwards through the incessant changes of a long course of development, undergone either in the womb or in the egg, and ultimately appear in the offspring when mature, or even when quite old, as in the case of certain diseases? Or again, what can be more wonderful than the well-ascertained fact that the minute ovule of a good milking cow will produce a male, from whom a cell, in union with an ovule, will produce a female, and she, when mature, will have large mammary glands, yielding an abundant supply of milk, and even milk of a particular quality? Nevertheless, the real subject of surprise is, as Sir H. Holland has well remarked (12/1. "Medical Notes and Reflections" 3rd edition 1855 page 267.) not that a character should be inherited, but that any should ever fail to be inherited. In a future chapter, devoted to an hypothesis which I have termed pangenesis, an attempt will be made to show the means by which characters of all kinds are transmitted from generation to generation.
Some writers (12/2. Mr. Buckle in his "History of Civilisation" expresses doubts on the subject, owing to the want of statistics. See also Mr. Bowen, Professor of Moral Philosophy, in "Proc. American Acad. of Sciences" volume 5 page 102.), who have not attended to natural history, have attempted to show that the force of inheritance has been much exaggerated. The breeders of animals would smile at such simplicity; and if they condescended to make any answer, might ask what would be the chance of winning a prize if two inferior animals were paired together? They might ask whether the half-wild Arabs were led by theoretical notions to keep pedigrees of their horses?
Why have pedigrees been scrupulously kept and published of the Shorthorn cattle, and more recently of the Hereford breed? Is it an illusion that these recently improved animals safely transmit their excellent qualities even when crossed with other breeds? have the Shorthorns, without good reason, been purchased at immense prices and exported to almost every quarter of the globe, a thousand guineas having been given for a bull? With greyhounds pedigrees have likewise been kept, and the names of such dogs, as s...o...b..ll, Major, etc., are as well known to coursers as those of Eclipse and Herod on the turf. Even with the Gamec.o.c.k, pedigrees of famous strains were formerly kept, and extended back for a century. With pigs, the Yorkshire and c.u.mberland breeders "preserve and print pedigrees;" and to show how such highly-bred animals are valued, I may mention that Mr. Brown, who won all the first prizes for small breeds at Birmingham in 1850, sold a young sow and boar of his breed to Lord Ducie for 43 guineas; the sow alone was afterwards sold to the Rev. F. Thursby for 65 guineas; who writes, "She paid me very well, having sold her produce for 300 pounds, and having now four breeding sows from her." (12/3. For greyhounds see Low "Domestic Animals of the British Islands" 1845 page 721. For game-fowls see "The Poultry Book" by Mr. Tegetmeier 1866 page 123. For pigs see Mr. Sidney"s edition of "Youatt on the Pig" 1860 pages 11, 22.) Hard cash paid down, over and over again, is an excellent test of inherited superiority. In fact, the whole art of breeding, from which such great results have been attained during the present century, depends on the inheritance of each small detail of structure. But inheritance is not certain; for if it were, the breeder"s art (12/4. "The Stud Farm" by Cecil page 39.) would be reduced to a certainty, and there would be little scope left for that wonderful skill and perseverance shown by the men who have left an enduring monument of their success in the present state of our domesticated animals.
It is hardly possible, within a moderate compa.s.s, to impress on the mind of those who have not attended to the subject, the full conviction of the force of inheritance which is slowly acquired by rearing animals, by studying the many treatises which have been published on the various domestic animals, and by conversing with breeders. I will select a few facts of the kind, which, as far as I can judge, have most influenced my own mind. With man and the domestic animals, certain peculiarities have appeared in an individual, at rare intervals, or only once or twice in the history of the world, but have reappeared in several of the children and grandchildren. Thus Lambert, "the porcupine-man," whose skin was thickly covered with warty projections, which were periodically moulted, had all his six children and two grandsons similarly affected. (12/5.
"Philosophical Transactions" 1755 page 23. I have seen only second-hand accounts of the two grandsons. Mr. Sedgwick, in a paper to which I shall hereafter often refer, states that FOUR generations were affected, and in each the males alone.) The face and body being covered with long hair, accompanied by deficient teeth (to which I shall hereafter refer), occurred in three successive generations in a Siamese family; but this case is not unique, as a woman (12/6. Barbara Van Beck, figured, as I am informed by the Rev. W.D. Fox, in Woodburn"s "Gallery of Rare Portraits" 1816 volume 2) with a completely hairy face who was exhibited in London in 1663, and another instance has recently occurred. Colonel Hallam (12/7. "Proc.
Zoolog. Soc." 1833 page 16.) has described a race of two-legged pigs, "the hinder extremities being entirely wanting;" and this deficiency was transmitted through three generations. In fact, all races presenting any remarkable peculiarity, such as solid-hoofed swine, Mauchamp sheep, niata cattle, etc., are instances of the long-continued inheritance of rare deviations of structure.
When we reflect that certain extraordinary peculiarities have thus appeared in a single individual out of many millions, all exposed in the same country to the same general conditions of life, and, again, that the same extraordinary peculiarity has sometimes appeared in individuals living under widely different conditions of life, we are driven to conclude that such peculiarities are not directly due to the action of the surrounding conditions, but to unknown laws acting on the organisation or const.i.tution of the individual;--that their production stands in hardly closer relation to the conditions of life than does life itself. If this be so, and the occurrence of the same unusual character in the child and parent cannot be attributed to both having been exposed to the same unusual conditions, then the following problem is worth consideration, as showing that the result cannot be due, as some authors have supposed, to mere coincidence, but must be consequent on the members of the same family inheriting something in common in their const.i.tution. Let it be a.s.sumed that, in a large population, a particular affection occurs on an average in one out of a million, so that the a priori chance that an individual taken at random will be so affected is only one in a million. Let the population consist of sixty millions, composed, we will a.s.sume, of ten million families, each containing six members. On these data, Professor Stokes has calculated for me that the odds will be no less than 8333 millions to 1 that in the ten million families there will not be even a single family in which one parent and two children will be affected by the peculiarity in question. But numerous instances could be given, in which several children have been affected by the same rare peculiarity with one of their parents; and in this case, more especially if the grandchildren be included in the calculation, the odds against mere coincidence become something prodigious, almost beyond enumeration.
In some respects the evidence of inheritance is more striking when we consider the reappearance of trifling peculiarities. Dr. Hodgkin formerly told me of an English family in which, for many generations, some members had a single lock differently coloured from the rest of the hair. I knew an Irish gentleman, who, on the right side of his head, had a small white lock in the midst of his dark hair: he a.s.sured me that his grandmother had a similar lock on the same side, and his mother on the opposite side. But it is superfluous to give instances; every shade of expression, which may often be seen alike in parents and children, tells the same story. On what a curious combination of corporeal structure, mental character, and training, handwriting depends! yet every one must have noted the occasional close similarity of the handwriting in father and son, although the father had not taught his son. A great collector of autographs a.s.sured me that in his collection there were several signatures of father and son hardly distinguishable except by their dates. Hofacker, in Germany, remarks on the inheritance of handwriting; and it has even been a.s.serted that English boys when taught to write in France naturally cling to their English manner of writing; but for so extraordinary a statement more evidence is requisite.
(12/8. Hofacker "Ueber die Eigenschaften" etc. 1828 s. 34. With respect to France, Report by Pariset in "Comptes Rendus" 1847 page 592.) Gait, gestures, voice, and general bearing are all inherited, as the ill.u.s.trious Hunter and Sir A. Carlisle have insisted. (12/9. Hunter as quoted in Harlan"s "Med. Researches" page 530. Sir A. Carlisle "Phil. Transact." 1814 page 94.) My father communicated to me some striking instances, in one of which a man died during the early infancy of his son, and my father, who did not see this son until grown up and out of health, declared that it seemed to him as if his old friend had risen from the grave, with all his highly peculiar habits and manners. Peculiar manners pa.s.s into tricks, and several instances could be given of their inheritance; as in the case, often quoted, of the father who generally slept on his back, with his right leg crossed over the left, and whose daughter, whilst an infant in the cradle, followed exactly the same habit, though an attempt was made to cure her. (12/10. Girou de Buzareingues "De la Generation" page 282. I have given an a.n.a.logous case in my book on "The Expression of the Emotions.") I will give one instance which has fallen under my own observation, and which is curious from being a trick a.s.sociated with a peculiar state of mind, namely, pleasureable emotion. A boy had the singular habit, when pleased, of rapidly moving his fingers parallel to each other, and, when much excited, of raising both hands, with the fingers still moving, to the sides of his face on a level with the eyes; when this boy was almost an old man, he could still hardly resist this trick when much pleased, but from its absurdity concealed it. He had eight children. Of these, a girl, when pleased, at the age of four and a half years, moved her fingers in exactly the same way, and what is still odder, when much excited, she raised both her hands, with her fingers still moving, to the sides of her face, in exactly the same manner as her father had done, and sometimes even still continued to do so when alone. I never heard of any one, excepting this one man and his little daughter, who had this strange habit; and certainly imitation was in this instance out of the question.
Some writers have doubted whether those complex mental attributes, on which genius and talent depend, are inherited, even when both parents are thus endowed. But he who will study Mr. Galton"s able work on "Hereditary Genius" will have its doubts allayed.
Unfortunately it matters not, as far as inheritance is concerned, how injurious a quality or structure may be if compatible with life. No one can read the many treatises (12/11. The works which I have read and found most useful are Dr. Prosper Lucas"s great work "Traite de l"Heredite Naturelle"
1847; Mr. W. Sedgwick in "British and Foreign Medico-Chirurg. Review" April and July 1861 and April and July 1863: Dr. Garrod on Gout is quoted in these articles. Sir Henry Holland "Medical Notes and Reflections" 3rd edition 1855. Piorry "De l"Heredite dans les Maladies" 1840. Adams "A Philosophical Treatise on Hereditary Peculiarities" 2nd edition 1815. Essay on "Hereditary Diseases" by Dr. J. Steinan 1843. See Paget in "Medical Times" 1857 page 192 on the Inheritance of Cancer; Dr. Gould in "Proc. of American Acad. of Sciences" November 8, 1853 gives a curious case of hereditary bleeding in four generations. Harlan "Medical Researches" page 593.) on hereditary disease and doubt this. The ancients were strongly of this opinion, or, as Ranchin expresses it, Omnes Graeci, Arabes, et Latini in eo consentiunt. A long catalogue could be given of all sorts of inherited malformations and of predisposition to various diseases. With gout, fifty per cent of the cases observed in hospital practice are, according to Dr. Garrod, inherited, and a greater percentage in private practice. Every one knows how often insanity runs in families, and some of the cases given by Mr. Sedgwick are awful,--as of a surgeon, whose brother, father, and four paternal uncles were all insane, the latter dying by suicide; of a Jew, whose father, mother, and six brothers and sisters were all mad; and in some other cases several members of the same family, during three or four successive generations, have committed suicide. Striking instances have been recorded of epilepsy, consumption, asthma, stone in the bladder, cancer, profuse bleeding from the slightest injuries, of the mother not giving milk, and of bad parturition being inherited. In this latter respect I may mention an odd case given by a good observer (12/12.
Marshall quoted by Youatt in his work on "Cattle" page 284.), in which the fault lay in the offspring, and not in the mother: in a part of Yorkshire the farmers continued to select cattle with large hind-quarters, until they made a strain called "Dutch-b.u.t.tocked," and "the monstrous size of the b.u.t.tocks of the calf was frequently fatal to the cow, and numbers of cows were annually lost in calving."
[Instead of giving numerous details on various inherited malformations and diseases, I will confine myself to one organ, that which is the most complex, delicate, and probably best-known in the human frame, namely, the eye, with its accessory parts. (12/13. Almost any other organ might have been selected. For instance Mr. J. Tomes "System of Dental Surgery" 2nd edition 1873 page 114 gives many instances with teeth, and others have been communicated to me.) To begin with the latter: I have received an account of a family in which one parent and the children are affected by drooping eyelids, in so peculiar a manner, that they cannot see without throwing their heads backwards. Mr. Wade, of Wakefield, has given me an a.n.a.logous case of a man who had not his eyelids thus affected at birth, nor owed their state, as far as was known, to inheritance, but they began to droop whilst he was an infant after suffering from fits, and he has transmitted the affection to two out of his three children, as was evident in the photographs of the whole family sent to me together with this account. Sir A. Carlisle (12/14. "Philosoph. Transact." 1814 page 94.) specifies a pendulous fold to the eyelids, as inherited. "In a family," says Sir H.
Holland (12/15. "Medical Notes and Reflections" 3rd edition page 33.) "where the father had a singular elongation of the upper eyelid, seven or eight children were born with the same deformity; two or three other children having it not." Many persons, as I hear from Sir J. Paget, have two or three hairs in their eyebrows much longer than the others; and even so trifling a peculiarity as this certainly runs in families.
With respect to the eye itself, the highest authority in England, Mr.
Bowman, has been so kind as to give me the following remarks on certain inherited imperfections. First, hypermetropia, or morbidly long sight: in this affection, the organ, instead of being spherical, is too flat from front to back, and is often altogether too small, so that the retina is brought too forward for the focus of the humours; consequently a convex gla.s.s is required for clear vision of near objects, and frequently even of distant ones. This state occurs congenitally, or at a very early age, often in several children of the same family, where one of the parents has presented it. (12/16. This affection, as I hear from Mr. Bowman, has been ably described and spoken of as hereditary by Dr. Donders of Utrecht, whose work was published in English by the Sydenham Society in 1864.) Secondly, myopia, or short-sight, in which the eye is egg-shaped and too long from front to back; the retina in this case lies behind the focus, and is therefore fitted to see distinctly only very near objects. This condition is not commonly congenital, but comes on in youth, the liability to it being well known to be transmissible from parent to child. The change from the spherical to the ovoidal shape seems the immediate consequence of something like inflammation of the coats, under which they yield, and there is ground for believing that it may often originate in causes acting on the individual affected (12/17. M. Giraud-Teulon has recently collected abundant statistical evidence, "Revue des Cours Scientifiques" September 1870 page 625, showing that short sight is due to the habit of viewing objects from a short distance, c"est le travail a.s.sidu, de pres.) and may thenceforward become transmissible. When both parents are myopic Mr. Bowman has observed the hereditary tendency in this direction to be heightened, and some of the children to be myopic at an earlier age or in a higher degree than their parents. Thirdly, squinting is a familiar example of hereditary transmission: it is frequently a result of such optical defects as have been above mentioned; but the more primary and uncomplicated forms of it are also sometimes in a marked degree transmitted in a family.
Fourthly, CATARACT, or opacity of the crystalline lens, is commonly observed in persons whose parents have been similarly affected, and often at an earlier age in the children than in the parents. Occasionally more than one child in a family is thus afflicted, one of whose parents or other relations, presents the senile form of the complaint. When cataract affects several members of a family in the same generation, it is often seen to commence at about the same age in each: e.g., in one family several infants or young persons may suffer from it; in another, several persons of middle age. Mr. Bowman also informs me that he has occasionally seen, in several members of the same family, various defects in either the right or left eye; and Mr. White Cooper has often seen peculiarities of vision confined to one eye reappearing in the same eye in the offspring. (12/18. Quoted by Mr. Herbert Spencer "Principles of Biology" volume 1 page 244.)
The following cases are taken from an able paper by Mr. W. Sedgwick, and from Dr. Prosper Lucas. (12/19. "British and Foreign Medico-Chirurg.
Review" April 1861 pages 482-6; "L"Hered. Nat." tome 1 pages 391-408.) Amaurosis, either congenital or coming on late in life, and causing total blindness, is often inherited; it has been observed in three successive generations. Congenital absence of the iris has likewise been transmitted for three generations, a cleft-iris for four generations, being limited in this latter case to the males of the family. Opacity of the cornea and congenital smallness of the eyes have been inherited. Portal records a curious case, in which a father and two sons were rendered blind, whenever the head was bent downwards, apparently owing to the crystalline lens, with its capsule, slipping through an unusually large pupil into the anterior chamber of the eye. Day-blindness, or imperfect vision under a bright light, is inherited, as is night-blindness, or an incapacity to see except under a strong light: a case has been recorded, by M. Cunier, of this latter defect having affected eighty-five members of the same family during six generations. The singular incapacity of distinguishing colours, which has been called DALTONISM, is notoriously hereditary, and has been traced through five generations, in which it was confined to the female s.e.x.
With respect to the colour of the iris: deficiency of colouring matter is well known to be hereditary in albinoes. The iris of one eye being of different colour from that of the other, and the iris being spotted, are cases which have been inherited. Mr. Sedgwick gives, in addition, on the authority of Dr. Osborne (12/20. Dr. Osborne, Pres. of Royal College of Phys. in Ireland, published this case in the "Dublin Medical Journal" for 1835.), the following curious instance of strong inheritance: a family of sixteen sons and five daughters all had eyes "resembling in miniature the markings on the back of a tortoisesh.e.l.l cat." The mother of this large family had three sisters and a brother all similarly marked, and they derived this peculiarity from their mother, who belonged to a family notorious for transmitting it to their posterity.
Finally, Dr. Lucas emphatically remarks that there is not one single faculty of the eye which is not subject to anomalies; and not one which is not subjected to the principle of inheritance. Mr. Bowman agrees with the general truth of this proposition; which of course does not imply that all malformations are necessarily inherited; this would not even follow if both parents were affected by an anomaly which in most cases was transmissible.]
Even if no single fact had been known with respect to the inheritance of disease and malformations by man, the evidence would have been ample in the case of the horse. And this might have been expected, as horses breed much quicker than man, are matched with care, and are highly valued. I have consulted many works, and the unanimity of the belief by veterinaries of all nations in the transmission of various morbid tendencies is surprising.
Authors who have had wide experience give in detail many singular cases, and a.s.sert that contracted feet, with the numerous contingent evils, of ring-bones, curbs, splints, spavin, founder and weakness of the front legs, roaring or broken and thick wind, melanosis, specific ophthalmia, and blindness (the great French veterinary Huzard going so far as to say that a blind race could soon be formed), crib-biting, jibbing and ill-temper, are all plainly hereditary. Youatt sums up by saying "there is scarcely a malady to which the horse is subject which is not hereditary;" and M.
Bernard adds that the doctrine "that there is scarcely a disease which does not run in the stock, is gaining new advocates every day." (12/21. These various statements are taken from the following works and papers:--Youatt on "The Horse" pages 35, 220. Lawrence "The Horse" page 30. Karkeek in an excellent paper in "Gard. Chronicle" 1853 page 92. Mr. Burke in "Journal of R. Agricul. Soc. of England" volume 5 page 511. "Encyclop. of Rural Sports"
page 279. Girou de Buzareingues "Philosoph. Phys." page 215. See following papers in "The Veterinary;" Roberts in volume 2 page 144; M. Marrimpoey volume 2 page 387; Mr. Karkeek volume 4 page 5; Youatt on Goitre in "Dogs"
volume 5 page 483: Youatt in volume 6 pages 66, 348, 412; M. Bernard volume 11 page 539; Dr. Samesreuther on "Cattle" in volume 12 page 181; Percivall in volume 13 page 47. With respect to blindness in horses see also a whole row of authorities in Dr. P. Lucas"s great work, tome 1 page 399. Mr. Baker in "The Veterinary" volume 13 page 721, gives a strong case of hereditary imperfect vision and of jibbing.) So it is in regard to cattle, with consumption, good and bad teeth, fine skin, etc. etc. But enough, and more than enough, has been said on disease. Andrew Knight, from his own experience, a.s.serts that disease is hereditary with plants; and this a.s.sertion is endorsed by Lindley. (12/22. Knight on "The Culture of the Apple and Pear" page 34. Lindley"s "Horticulture" page 180.)
Seeing how hereditary evil qualities are, it is fortunate that good health, vigour, and longevity are equally inherited. It was formerly a well-known practice, when annuities were purchased to be received during the life-time of a nominee, to search out a person belonging to a family of which many members had lived to extreme old age. As to the inheritance of vigour and endurance, the English race-horse offers an excellent instance. Eclipse begot 334, and King Herod 497 winners. A "c.o.c.k-tail" is a horse not purely bred, but with only one-eighth, or one-sixteenth impure blood in his veins, yet very few instances have ever occurred of such horses having won a great race. They are sometimes as fleet for short distances as thoroughbreds, but as Mr. Robson, the great trainer, a.s.serts, they are deficient in wind, and cannot keep up the pace. Mr. Lawrence also remarks, "perhaps no instance has ever occurred of a three-part-bred horse saving his "DISTANCE" in running two miles with thoroughbred racers." It has been stated by Cecil, that when unknown horses, whose parents were not celebrated, have unexpectedly won great races, as in the case of Priam, they can always be proved to be descended, on both sides, through many generations, from first-rate ancestors. On the Continent, Baron Cameronn challenges, in a German veterinary periodical, the opponents of the English race-horse to name one good horse on the Continent, which has not some English race-blood in his veins. (12/23. These statements are taken from the following works in order:--Youatt on "The Horse" page 48; Mr. Darvill in "The Veterinary"
volume 8 page 50. With respect to Robson see "The Veterinary" volume 3 page 580; Mr. Lawrence on "The Horse" 1829 page 9; "The Stud Farm" by Cecil 1851; Baron Cameronn quoted in "The Veterinary" volume 10 page 500.)
With respect to the transmission of the many slight, but infinitely diversified characters, by which the domestic races of animals and plants are distinguished, nothing need be said; for the very existence of persistent races proclaims the power of inheritance.
A few special cases, however, deserve some consideration. It might have been antic.i.p.ated, that deviations from the law of symmetry would not have been inherited. But Anderson (12/24. "Recreations in Agriculture and Nat.
Hist." volume 1 page 68.) states that a rabbit produced in a litter a young animal having only one ear; and from this animal a breed was formed which steadily produced one-eared rabbits. He also mentions a b.i.t.c.h with a single leg deficient, and she produced several puppies with the same deficiency.
From Hofacker"s account (12/25. "Ueber die Eigenschaften" etc. 1828 s.
107.) it appears that a one-horned stag was seen in 1781 in a forest in Germany, in 1788 two, and afterwards, from year to year, many were observed with only one horn on the right side of the head. A cow lost a horn by suppuration (12/26. Bronn "Geschichte der Natur" b. 2 s. 132.), and she produced three calves which had on the same side of the head, instead of a horn, a small bony lump attached merely to the skin; but we here encroach on the subject of inherited mutilations. A man who is left-handed, and a sh.e.l.l in which the spire turns in the wrong directions, are departures from the normal asymmetrical condition, and they are well-known to be inherited.
[POLYDACTYLISM.