The eighteenth century, though one of great intellectual activity, was, however, as regards cosmology, geology, general physiology or biology, a period of groping in the dim twilight, when the whole truth or even a part of it was beyond the reach of the greatest geniuses, and they could only seize on half-truths. Lamarck, both a practical botanist, systematic zoologist, and synthetic philosopher, had done his best work before the rise of the experimental and inductive methods, when direct observation and experiments had begun to take the place of vague _a priori_ thinking and reasoning, so that he labored under a disadvantage due largely to the age in which he lived.
Only the closing years of the century witnessed the rise of the experimental methods in physics and chemistry, owing to the brilliant work of Priestley and of Lavoisier. The foundations of general physiology had been laid by Haller,[109] those of embryology to a partial extent by Wolff,[110] Von Baer"s work not appearing until 1829, the year in which Lamarck died.
_Spontaneous Generation._--Lamarck"s views on spontaneous generation are stated in his _Recherches sur l"Organisation des Corps vivans_ (1802).
He begins by referring to his statement in a previous work[111] that life may be suspended for a time and then go on again.
"Here I would remark it (life) can be produced (_preparee_) both by an organic act and by nature herself, without any act of this kind, in such a way that certain bodies without possessing life can be prepared to receive it, by an impression _which indicates in these bodies the first traces of organization_."
We will not enter upon an exposition of his views on the nature of s.e.xual generation and of fecundation, the character of his _vapeur subtile_ (_aura vitalis_) which he supposes to take an active part in the act of fertilization, because the notion is quite as objectionable as that of the vital force which he rejects. He goes on to say, however, that we cannot penetrate farther into the wonderful mystery of fecundation, but the opinions he expresses lead to the view that "nature herself imitates her procedures in fecundation in another state of things, without having need of the union or of the products of any preexistent organization."
He proceeds to observe that in the places where his _aura vitalis_, or subtle fluid, is very abundant, as in hot climates or in heated periods, and especially in humid places, life seems to originate and to multiply itself everywhere and with a singular rapidity.
"In this high temperature the higher animals and mankind develop and mature more rapidly, and diseases run their courses more swiftly; while on the other hand these conditions are more favorable to the simpler forms of life, for the reason that in them the o.r.g.a.s.m and irritability are entirely dependent on external influences, and all plants are in the same case, because heat, moisture, and light complete the conditions necessary to their existence.
"Because heat is so advantageous to the simplest animals, let us examine whether there is not occasion for believing that it can itself form, with the concourse of favorable circ.u.mstances, the first germs of animal life.
"_Nature necessarily forms generations, spontaneous or direct, at the extremity of each organic kingdom or where the simplest organic bodies occur._"
This proposition, he allows, is so far removed from the view generally held, that it will be for a long time, and perhaps always, regarded as one of the errors of the human mind.
"I do not," he adds, "ask any one to accord it the least confidence on my word alone. But as surely it will happen, sooner or later, that men on the one hand independent of prejudices even the most widespread, and on the other profound observers of nature, may have a glimpse of this truth, I am very content that we should know that it is of the number of those views which, in spite of the prejudices of my age, I have thought it well to accept."
"Why," he asks, "should not heat and electricity act on certain matters under favorable conditions and circ.u.mstances?" He quotes Lavoisier as saying (_Chemie_, i., p. 202) "that G.o.d in creating light had spread over the world the principle of organization of feeling and of thought"; and Lamarck suggests that heat, "this mother of generation, this material soul of organized bodies," may be the chief one of the means which nature directly employs to produce in the appropriate kind of matter an act of arrangement of parts, of a primitive germ of organization, and consequently of vitalization a.n.a.logous to s.e.xual fecundation.
"Not only the direct formation of the simplest living beings could have taken place, as I shall attempt to demonstrate, but the following considerations prove that it is necessary that such germ-formations should be effected and be repeated under favorable conditions, without which the state of things which we observe could neither exist nor subsist."
His argument is that in the lower polyps (the Protozoa) there is no s.e.xual reproduction, no eggs. But they perish (as he strangely thought, without apparently attempting to verify his belief) in the winter. How, he asks, can they reappear? Is it not more likely that these simple organisms are themselves regenerated? After much verbiage and repet.i.tion, he concludes:
"We may conceive that the simplest organisms can arise from a minute ma.s.s of substances which possess the following conditions--namely, which will have solid parts in a state nearest the fluid conditions, consequently having the greatest suppleness and only sufficient consistence to be susceptible of const.i.tuting the parts contained in it. Such is the condition of the most gelatinous organized bodies.
"Through such a ma.s.s of substances the subtile and expansive fluids spread, and, always in motion in the milieu environing it, unceasingly penetrate it and likewise dissipate it, arranging while traversing this ma.s.s the internal disposition of its parts, and rendering it suitable to continually absorb and to exhale the other environing fluids which are able to penetrate into its interior, and which are susceptible of being contained.
"These other fluids, which are water charged with dissolved (_dissous_) gas, or with other tenuous substances, the atmospheric air, which contains water, etc., I call containable fluids, to distinguish them from subtile fluids, such as caloric, electricity, etc., which no known bodies are believed to contain.
"The containable fluids absorbed by the small gelatinous ma.s.s in question remain almost motionless in its different parts, because the non-containable subtile fluids which always penetrate there do not permit it.
"In this way the uncontainable fluids at first mark out the first traces of the simplest organization, and consequently the containable fluids by their movements and their other influences develop it, and with time and all the favorable circ.u.mstances complete it."
This is certainly a sufficiently vague and unsatisfactory theory of spontaneous generation. This sort of guess-work and hypothetical reasoning is not entirely confined to Lamarck"s time. Have we not, even a century later, examples among some of our biologists, and very eminent ones, of whole volumes of _a priori_ theorizing and reasoning, with scarcely a single new fact to serve as a foundation? And yet this is an age of laboratories, of experimentations and of trained observers. The best of us indulge in far-fetched hypotheses, such as pangenesis, panmixia, the existence of determinants, and if this be so should we not excuse Lamarck, who gave so many years to close observation in systematic botany and zoology, for his flights into the empyrean of subtle fluids, containable and uncontainable, and for his invocation of an _aura vitalis_, at a time when the world of demonstrated facts in modern biology was undiscovered and its existence unsuspected?
_The Preexistence of Germs and the Encas.e.m.e.nt Theory._--Lamarck did not believe in Bonnet"s idea of the "preexistence of germs." He asks whether there is any foundation for the notion that germs "successively develop in generations, _i.e._ in the multiplication of individuals for the preservation of species," and says:
"I am not inclined to believe it if this preexistence is taken in a general sense; but in limiting it to individuals in which the unfertilized embryos or germs are formed before generation. I then believe that it has some foundation.--They say with good reason," he adds, "that every living being originates from an egg.... But the eggs being the envelope of every kind of germ, they preexist in the individuals which produce them, before fertilization has vivified them. The seeds of plants (which are vegetable eggs) actually exist in the ovaries of flowers before the fertilization of these ovaries."[112]
From whom did he get this idea that seeds or eggs are envelopes of all sorts of germs? It is not the "evolution" of a single germ, as, for example, an excessively minute but complete chick in the hen"s egg, in the sense held by Bonnet. Who it was he does not mention. He evidently, however, had the Swiss biologist in mind, who held that all living things proceed from preexisting germs.[113]
Whatever may have been his views as to the germs in the egg before fertilization, we take it that he believed in the epigenetic development of the plant or animal after the seed or egg was once fertilized.[114]
Lamarck did not adopt the encas.e.m.e.nt theory of Swammerdam and of h.e.l.ler.
We find nothing in Lamarck"s writings opposed to epigenesis. The following pa.s.sage, which bears on this subject, is translated from his _Memoires de Physique_ (p. 250), where he contrasts the growth of organic bodies with that of minerals.
"The body of this living being not having been formed by _juxtaposition_, as most mineral substances, that is to say, by the external and successive apposition of particles aggregated _en ma.s.se_ by attraction, but essentially formed by generation, in its principle, it has then grown by intussusception--namely, by the introduction, the transportation, and the internal apposition of molecules borne along and deposited between its parts; whence have resulted the successive developments of parts which compose the body of this living individual, and from which afterwards also result the repairs which preserve it during a limited time."
Here, as elsewhere in his various works, Lamarck brings out the fact, for the first time stated, that all material things are either non-living or mineral, inorganic; or living, organic. A favorite phrase with him is living bodies, or, as we should say, organisms. He also is the first one to show that minerals increase by juxtaposition, while organisms grow by intussusception.
No one would look in his writings for an idea or suggestion of the principle of differentiation of parts or organs as we now understand it, or for the idea of the physiological division of labor; these were reserved for the later periods of embryology and morphology.
_Origin of the First Vital Function._--We will now return to the germ.
After it had begun spontaneous existence, Lamarck proceeds to say:
"Before the containable fluids absorbed by the small, jelly-like ma.s.s in question have been expelled by the new portions of the same fluids which reach there, they can then deposit certain of the contained fluids they carry along, and the movements of the contained fluids may apply these substances to the containing parts of the newly organized microscopic being. In this way originates the first of the vital functions which becomes established in the simplest organism, _i.e._, nutrition. The environing containable fluids are, then, for the living body of very great simplicity, a veritable chyle entirely prepared by nature.
"Mutilation cannot operate without gradually increasing the consistence of the parts contained within the minute new organism and without extending its dimensions. Hence soon arose the second of the vital functions, _growth or internal development_."
_First Faculty of Animal Nature._--Then gradually as the continuity of this state of things within the same minute living ma.s.s in question increases the consistence of its parts enclosed within and extends its dimensions, a vital o.r.g.a.s.m, at first very feeble, but becoming progressively more intense, is formed in these enclosed parts and renders them susceptible of _reaction_ against the slight impression of the fluids in motion which they contain, and at the same time renders them capable of contraction and of distention. Hence the origin of _animal irritability_ and the basis of feeling, which is developed wherever a nervous fluid, susceptible of locating the effects in one of several special centres, can be formed.
"Scarcely will the living corpuscle, newly animalized, have received any increase in consistence and in dimensions of the parts contained, when, as the result of the organic movement which it enjoys, it will be subjected to successive changes and losses of its substance.
"It will then be obliged to take nourishment not only to obtain any development whatever, but also to preserve its individual existence, because it is necessary that it repair its losses under penalty of its destruction.
"But as the individual in question has not yet any special organ for nutrition, it therefore absorbs by the pores of its internal surface the substance adapted for its nourishment. Thus the first mode of taking food in a living body so simple can be no other than by absorption or a sort of suction, which is accomplished by the pores of its outer surface.
"This is not all; up to the present time the animalized corpuscle we are considering is still only a primitive animalcule because it as yet has no special organ. Let us see then how nature will come to furnish it with any primitive special organ, and what will be the organ that nature will form before any others, and which in the simplest animal is the only one constantly found; this is the alimentary ca.n.a.l, the princ.i.p.al organ of digestion common to all except colpodes, vibrios, proteus (amoeba), volvoces, monads, etc.
"This digestive ca.n.a.l is," he says--proceeding with his _a priori_ morphology--"a little different from that of this day, produced by contractions of the body, which are stronger in one part of the body than in another, until a little crease is produced on the surface of the body. This furrow or crease will receive the food. Insensibly this little furrow by the habit of being filled, and by the so frequent use of its pores, will gradually increase in depth; it will soon a.s.sume the form of a pouch or of a tubular cavity with porous walls, a blind sac, or with but a single opening. Behold the primitive alimentary ca.n.a.l created by nature, the simplest organ of digestion."
In like _a priori_ manner he describes the creation of the faculty of reproduction. The next organ, he says, is that of reproduction due to the regenerative faculty. He describes fission and budding. Finally (p. 122) he says:
"Indeed, we perceive that if the first germs of living bodies are all formed in one day in such great abundance and facility under favorable circ.u.mstances, they ought to be, nevertheless, by reason of the antiquity of the causes which make them exist, the most ancient organisms in nature."
In 1794 he rejected the view once held of a continuous chain of being, the _ech.e.l.le des etres_ suggested by Locke and by Leibnitz, and more fully elaborated by Bonnet, from the inorganic to the organic worlds, from minerals to plants, from plants to polyps (our Infusoria), polyps to worms, and so on to the higher animals. He, on the contrary, affirms that nature makes leaps, that there is a wide gap between minerals and living bodies, that everything is not gradated and shaded into each other. One reason for this was possibly his strange view, expressed in 1794, that all brute bodies and inorganic matters, even granite, were not formed at the same epoch but at different times, and were derived from organisms.[115]
The mystical doctrine of a vital force was rife in Lamarck"s time. The chief starting point of the doctrine was due to Haller, and, as Verworn states, it is a doctrine which has confused all physiology down to the middle of the present century, and even now emerges again here and there in varied form.[116]
Lamarck was not a vitalist. Life, he says,[117] is usually supposed to be a particular being or ent.i.ty; a sort of principle whose nature is unknown, and which possesses living bodies. This notion he denies as absurd, saying that life is a very natural phenomenon, a physical fact; in truth a little complicated in its principles, but not in any sense a particular or special being or ent.i.ty.
He then defines life in the following words: "Life is an order and a state of things in the parts of every body possessing it, which permits or renders possible in it the execution of organic movement, and which, so long as it exists, is effectively opposed to death. Derange this order and this state of things to the point of preventing the execution of organic movement, or the possibility of its reestablishment, then you cause death." Afterwards, in the _Philosophie zoologique_, he modifies this definition, which reads thus: "Life, in the parts of a body which possesses it, is an order and a state of things which permit organic movements; and these movements, which const.i.tute active life, result from the action of a stimulating cause which excites them."[118]
For the science of all living bodies Lamarck proposed the word "Biology," which is so convenient a term at the present day. The word first appears in the preface to the _Hydrogeologie_, published in 1802.
It is worthy of note that in the same year the same word was proposed for the same science by G. R. Trevira.n.u.s as the t.i.tle of a work, _Biologie, der Philosophie der lebenden Natur_, published in 1802-1805 (vols. i.-vi., 1802-1822), the first volume appearing in 1802.
In the second part of the _Philosophie zoologique_ he considers the physical causes of life, and in the introduction he defines nature as the _ensemble_ of objects which comprise: (1) All existing physical bodies; (2) the general and special laws which regulate the changes of condition and situation of these bodies; (3) finally, the movement everywhere going on among them resulting in the wonderful order of things in nature.
To regard nature as eternal, and consequently as having existed from all time, is baseless and unreasonable. He prefers to think that nature is only a result, "whence, I suppose, and am glad to admit, a first cause, in a word, a supreme power which has given existence to nature, which has made it as a whole what it is."
As to the source of life in bodies endowed with it, he considers it a problem more difficult than to determine the course of the stars in s.p.a.ce, or the size, ma.s.ses, and movements of the planets belonging to our solar system; but, however formidable the problem, the difficulties are not insurmountable, as the phenomena are purely physical--_i.e._, essentially resulting from acts of organization.
After defining life, in the third chapter (beginning vol. ii.) he treats of the exciting cause of organic movements. This exciting cause is foreign to the body which it vivifies, and does not perish, like the latter. "This cause resides in invisible, subtile, expansive, ever-active fluids which penetrate or are incessantly developed in the bodies which they animate." These subtile fluids we should in these days regard as the physico-chemical agents, such as heat, light, electricity.