But why should not a germ disease be always fatal? If the bacteria thus take possession of the body and can grow there, why do they not always continue to multiply until they produce sufficient poison to destroy the life of the individual? Such fatal results do, of course, occur, but in by far the larger proportion of cases recovery finally takes place.
Plainly, the body must have another set of resisting forces which is concerned in the final recovery. Although weakened by the poisoning and suffering from the disease, it does not yield the battle, but somewhat slowly organizes a new attack upon the invaders. For a time the multiplying bacteria have an unimpeded course and grow rapidly; but finally their further increase is checked, their vigour impaired, and after this they diminish in numbers and are finally expelled from the body entirely. Of the nature of this new resistance but little is yet known. We notice, in the first place, that commonly after such a recovery the individual has decidedly increased resistance to the disease. This increased resistance may be very lasting, and may be so considerable as to give almost complete immunity from the disease for many years, or for life. One attack of scarlet fever gives the individual great immunity for the future. On the other hand, the resistance thus derived may be very temporary, as in the case of diphtheria. But a certain amount of resistance appears to be always acquired. This power of resisting the activities of the parasites seems to be increased during the progress of the disease, and, if it becomes sufficient, it finally drives off the bacteria before they have produced death. After this, recovery takes place. To what this newly acquired resisting power is due is by no means clear to bacteriologists, although certain factors are already known. It appears beyond question that in the case of certain diseases the cells of the body after a time produce substances which serve as antidotes to the poisons produced by the bacteria during their growth in the body-ant.i.toxines. In the case of diphtheria, for instance, the germs growing in the throat produce poisons which are absorbed by the body and give rise to the symptoms of the disease; but after a time the body cells react, and themselves produce a counter toxic body which neutralizes the poisonous effect of the diphtheria poison. This substance has been isolated from the blood of animals that have recovered from an attack of diphtheria, and has been called diphtheria ant.i.toxine. But even with this knowledge the recovery is not fully explained. This ant.i.toxine neutralizes the effects of the diphtheria toxine, and then the body develops strength to drive off the bacteria which have obtained lodgment in the throat.
How they accomplish this latter achievement we do not know as yet.
The ant.i.toxme developed simply neutralizes the effects of the toxine. Some other force must be at work to get rid of the bacteria, a force which can only exert itself after the poisoning effect of the poison is neutralized. In these cases, then, the recovery is due, first, to the development in the body of the natural antidotes to the toxic poisons, and, second, to some other unknown force which drives off the parasites.
These facts are certainly surprising. If one had been asked to suggest the least likely theory to explain recovery from disease, he could hardly have found one more unlikely than that the body cells developed during the disease an antidote to the poison which the disease bacteria were producing. Nevertheless, it is beyond question that such antidotes are formed during the course of the germ diseases. It has not yet been shown in all diseases, and it would be entirely too much to claim that this is the method of recovery in all cases. We may say, however, in regard to bacterial diseases in general, that after the bacteria enter the body at some weak point they have first a battle to fight with the resisting powers of the body, which appear to be partly biological and partly chemical. These resisting powers are in many cases entirely sufficient to prevent the bacteria from obtaining a foothold. If the invading host overcome the resisting powers, then they begin to multiply rapidly, and take possession of the body or some part of it. They continue to grow until either the individual dies or something occurs to check their growth. After the individual develops the renewed powers of checking their growth, recovery takes place, and the individual is then, because of these renewed powers of resistance, immune from a second attack of the disease for a variable length of time.
This, in the merest outline, represents the relation of bacterial parasites to the human body But while this is a fair general expression of the matter, it must be recognised that different diseases differ much in their relations, and no general outline will apply to all They differ in their method of attack and in the point of attack. Not only do they produce different kinds of poisons giving rise to different symptoms of poisoning; not only do they produce different results in different animals; not only do the different pathogenic species differ much in their power to develop serious disease, but the different species are very particular as to what species of animal they attack. Some of them can live as parasites in man alone; some can live as parasites upon man and the mouse and a few other animals; some can live in various animals but not in man; some appear to be able to live in the field mouse, but not in the common mouse; some live in the horse; some in birds, but not in warm-blooded mammals; while others, again, can live almost equally well in the tissues of a long list of animals. Those which can live as parasites upon man are, of course, especially related to human disease, and are of particular interest to the physician, while those which live in animals are in a similar way of interest to veterinarians.
Thus we see that parasitic bacteria show the widest variations.
They differ in point of attack, in method of attack, and in the part of the body which they seize upon as a nucleus for growth.
They differ in violence and in the character of the poisons they produce, as well as in their power of overcoming the resisting powers of the body. They differ at different times in their powers of producing disease. In short, they show such a large number of different methods of action that no general statements can be made which will apply universally, and no one method of guarding against them or in driving them off can be hoped to apply to any extended list of diseases.
DISEASES CAUSED BY OTHER ORGANISMS THAN BACTERIA.
Although the purpose of this work is to deal primarily with the bacterial world, it would hardly be fitting to leave the subject without some reference to diseases caused by organisms which do not belong to the group of bacteria. While most of the so-called germ diseases are caused by the bacteria which we have been studying in the previous chapters, there are some whose inciting cause is to be found among organisms belonging to other groups.
Some of these are plants of a higher organization than bacteria, but others are undoubtedly microscopic animals. Their life habits are somewhat different from those of bacteria, and hence the course of the diseases is commonly different. Of the diseases thus produced by microscopic animals or by higher plants, one or two are of importance enough to deserve special mention here.
Malaria.--The most important of these diseases is malaria in its various forms, and known under various names--chills and fever, autumnal fever, etc. This disease, so common almost everywhere, has been studied by physicians and scientists for a long time, and many have been the causes a.s.signed to it. At one time it was thought to be the result of the growth of a bacterium, and a distinct bacillus was described as producing it. It has finally been shown, however, to be caused by a microscopic organism belonging to the group of unicellular animals, and somewhat closely related to the well-known amoeba. This organism is shown in Fig. 34. The whole history of the malarial organism is not yet known. The following statements comprise the most important facts known in regard to it, and its relation to the disease in man.
Undoubtedly the malarial germ has some home outside the human body, but it is not yet very definitely known what this external home is; nor do we know from what source the human parasite is derived. It appears probable that water serves in some cases as its means of transference to man, and air in other cases. From some external source it gains access to man and finds its way into the blood. Here it attacks the red blood-corpuscles, each malarial organism making its way into a single one (Fig. 340). Here it now grows, increasing in size at the expense of the substance of the corpuscle. As it becomes larger it becomes granular, and soon shows a tendency to separate into a number of irregular ma.s.ses.
Finally it breaks up into many minute bodies called spores. These bodies break out of the corpuscle and for a time live a free life in the blood. After a time they make their way into other red blood-corpuscles, develop into new malarial amoeboid parasites, and repeat the growth and sporulation. This process can apparently be repeated many times without check.
These organisms are thus to be regarded as parasites of the red corpuscles. It is, of course, easy to believe that an extensive parasitism and destruction of the corpuscles would be disastrous to the health of the individual, and the severity of the disease will depend upon the extent of the parasitism. Corresponding to this life history of the organism, the disease malaria is commonly characterized by a decided intermittency, periods of chill and fever alternating with periods of intermission in which these symptoms are abated. The paroxysms of the disease, characterized by the chill, occur at the time that the spores are escaping from the blood-corpuscles and floating in the blood. After they have again found their way into a blood-corpuscle the fever diminishes, and during their growth in the corpuscle until the next sporulation the individual has a rest from the more severe symptoms.
There appears to be more than one variety of the malarial organism, the different types differing in the length of time it takes for their growth and sporulation. There is one variety, the most common one, which requires two days for its growth, thus giving rise to the paroxysm of the disease about once in forty- eight hours; another variety appears to require three days for its growth; while still another variety appears to be decidedly irregular in its period of growth and sporulation. These facts readily explain some of the variations in the disease. Certain other irregularities appear to be due to a different cause. More than one brood of parasites may be in the blood of the individual at the same time, one producing sporulation at one time and another at a different time. Such a simultaneous growth of two independent broods may plainly produce almost any kind of modification in the regularity of the disease.
The malarial organism appears to be very sensitive to quinine, a very small quant.i.ty being sufficient to kill it. Upon this point depends the value of quinine as a medicine. If the drug be present in the blood at the time when the spores are set free from the blood-corpuscle, they are rapidly killed by it before they have a chance to enter another corpuscle. During their growth in the corpuscle they are far less sensitive to quinine than when they exist in the free condition as spores, and at this time the drug has little effect.
The malarial organism is an animal, and can not be cultivated in the laboratory by any artificial method yet devised. Its whole history is therefore not known. It doubtless has some home outside the blood of animals, and very likely it may pa.s.s through other stages of a metamorphosis in the bodies of other animals. Most parasitic animals have two or more hosts upon which they live, alternating from one to the other, and that such is the case with the malarial parasite is at least probable. But as yet bacteriologists have been unable to discover anything very definite in regard to the matter. Until we can learn something in regard to its life outside the blood of man we can do little in the way of devising methods to avoid it.
Malaria differs from most germ diseases in the fact that the organisms which produce it are not eliminated from the body in any way. In most germ diseases the germs are discharged from the patient by secretions or excretions of some kind, and from these excretions may readily find their way into other individuals. The malarial organism is not discharged from the body in any way, and hence is not contagious. If the parasite does pa.s.s part of its history in some other animal than man, there must be some means by which it pa.s.ses from man to its other host. It has been suggested that some of the insects which feed upon human blood may serve as the second host and become inoculated when feeding upon such blood. This has been demonstrated with startling success in regard to the mosquito (Anopheles), some investigators going so far as to say that this is the only way in which the disease can be communicated.
Several other microscopic animals occur as parasites upon man, and some of them are so definitely a.s.sociated with certain diseases as to lead to the belief that they are the cause of these diseases.
The only one of very common occurrence is a species known as Amaeba coli, which is found in cases of dysentery. In a certain type of dysentery this organism is so universally found that there is little doubt that it is in some very intimate way a.s.sociated with the cause of the disease. Definite proof of the matter is, however, as yet wanting.
On the side of plants, we find that several plants of a higher organization than bacteria may become parasitic upon the body of man and produce various types of disease. These plants belong mostly to the same group as the moulds, and they are especially apt to attack the skin. They grow in the skin, particularly under the hair, and may send their threadlike branches into some of the subdermal tissues. This produces irritation and inflammation of the skin, resulting in trouble, and making sores difficult to heal. So long as the plant continues to grow, the sores, of course, can not be healed, and when the organisms get into the skin under the hair it is frequently difficult to destroy them.
Among the diseases thus caused are ringworm, thrush, alopecia, etc.
CHAPTER VI.
METHODS OF COMBATING PARASITIC BACTERIA.
The chief advantage of knowing the cause of disease is that it gives us a vantage ground from which we may hope to find means of avoiding its evils. The study of medicine in the past history of the world has been almost purely empirical, with a very little of scientific basis. Great hopes are now entertained that these new facts will place this matter upon a more strictly scientific foundation. Certainly in the past twenty-five years, since bacteriology has been studied, more has been done to solve problems connected with disease than ever before. This new knowledge has been particularly directed toward means of avoiding disease. Bacteriology has thus far borne fruit largely in the line of preventive medicine, although to a certain extent also along the line of curative medicine. This chapter will be devoted to considering how the study of bacteriology has contributed directly and indirectly to our power of combating disease.
PREVENTIVE MEDICINE.
In the study of medicine in the past centuries the only aim has been to discover methods of curing disease; at the present time a large and increasing amount of study is devoted to the methods of preventing disease. Preventive medicine is a development of the last few years, and is based almost wholly upon our knowledge of bacteria. This subject is yearly becoming of more importance.
Forewarned is forearmed, and it has been found that to know the cause of a disease is a long step toward avoiding it. As some of our contagious and epidemic diseases have been studied in the light of bacteriological knowledge, it has been found possible to determine not only their cause, but also how infection is brought about, and consequently how contagion may be avoided. Some of the results which have grown up so slowly as to be hardly appreciated are really great triumphs. For instance, the study of bacteriology first led us to suspect, and then demonstrated, that tuberculosis is a contagious disease, and from the time that this was thus proved there has been a slow, but, it is hoped, a sure decline in this disease. Bacteriological study has shown that the source of cholera infection in cases of raging epidemics is, in large part at least, our drinking water; and since this has been known, although cholera has twice invaded Europe, and has been widely distributed, it has not obtained any strong foothold or given rise to any serious epidemic except in a few cases where its ravages can be traced to recognised carelessness. It is very significant to compare the history of the cholera epidemics of the past few years with those of earlier dates. In the epidemics of earlier years the cholera swept ruthlessly through communities without check. In the last few years, although it has repeatedly knocked at the doors of many European cities, it has been commonly confined to isolated cases, except in a few instances where these facts concerning the relation to drinking water were ignored.
The study of preventive medicine is yet in its infancy, but it has already accomplished much. It has developed modern systems of sanitation, has guided us in the building of hospitals, given rules for the management of the sick-room which largely prevent contagion from patient to nurse; it has told us what diseases are contagious, and in what way; it has told us what sources of contagion should be suspected and guarded against, and has thus done very much to prevent the spread of disease. Its value is seen in the fact that there has been a constant decrease in the death rate since modern ideas of sanitation began to have any influence, and in the fact that our general epidemics are less severe than in former years, as well as in the fact that more people escape the diseases which were in former times almost universal.
The study of preventive medicine takes into view several factors, all connected with the method and means of contagion. They are the following:
The Source of Infectious Material.--t has been learned that for most diseases the infectious material comes from individuals suffering with the disease, and that except in a few cases, like malaria, we must always look to individuals suffering from disease for all sources of contagion. It is found that pathogenic bacteria are in all these cases eliminated from the patient in some way, either from the alimentary ca.n.a.l or from skin secretions or otherwise, and that any nurse with common sense can have no difficulty in determining in what way the infectious material is eliminated from her patients. When this fact is known and taken into consideration it is a comparatively easy matter to devise valuable precautions against distribution of such material. It is thus of no small importance to remember that the simple presence of bacteria in food or drink is of no significance unless these bacteria have come from some source of disease infection.
The Method of Distribution.--The bacteria must next get from the original source of the disease to the new susceptible individual.
Bacteria have no independent powers of distribution unless they be immersed in liquids, and therefore their pa.s.sage from individual to individual must be a pa.s.sive one. They are readily transferred, however, by a number of different means, and the study of these means is aiding much in checking contagion Study along this line has shown that the means by which bacteria are carried are several. First we may notice food as a distributor.
Food may become contaminated by infectious material in many ways; for example, by contact with sewage, or with polluted water, or even with eating utensils which have been used by patients. Water is also likely to be contaminated with infectious material, and is a fertile source for distributing typhoid and cholera. Milk may become contaminated in a variety of ways, and be a source of distributing the bacteria which produce typhoid fever, tuberculosis, diphtheria, scarlet fever, and a few other less common diseases. Again, infected clothing, bedding, or eating utensils may be taken from a patient and be used by another individual without proper cleansing. Direct contact, or contact with infected animals, furnishes another method. Insects sometimes carry the bacteria from person to person, and in some diseases (tuberculosis, and perhaps scarlet fever and smallpox) we must look to the air as a distributor of the infectious material.
Knowledge of these facts is helping to account for mult.i.tudes of mysterious cases of infection, especially when we combine them with the known sources of contagious matter.
Means of Invasion.--Bacteriology has shown us that different species of parasitic bacteria have different means of entering the body, and that each must enter the proper place in order to get a foothold. After we learn that typhoid infectious material must enter the mouth in order to produce the disease; that tuberculosis may find entrance through the nose in breathing, while types of blood poisoning enter only through wounds or broken skin, we learn at once fundamental facts as to the proper methods of meeting these dangers. We learn that with some diseases care exercised to prevent the swallowing of infectious material is sufficient to prevent contagion, while with others this is entirely insufficient. When all these facts are understood it is almost always perfectly possible to avoid contagion; and as these facts become more and more widely known direct contagion is sure to become less frequent.
Above all, it is telling us what becomes of the pathogenic bacteria after being eliminated from the body of the patient; how they may exist for a long time still active; how they may lurk in filth or water dormant but alive, or how they may even multiply there. Preventive medicine is telling us how to destroy those thus lying in wait for a chance of infection, by discovering disinfectants and telling us especially where and when to use them. It has already taught us how to crush out certain forms of epidemics by the proper means of destroying bacteria, and is lessening the dangers from contagious diseases. In short, the study of bacteriology has brought us into a condition where we are no longer helpless in the presence of a raging epidemic. We no longer sit in helpless dismay, as did our ancestors, when an epidemic enters a community, but, knowing their causes and sources, set about at once to remove them. As a result, severe epidemics are becoming comparatively short-lived.
BACTERIA IN SURGERY.
In no line of preventive medicine has bacteriology been of so much value and so striking in its results as in surgery. Ever since surgery has been practised surgeons have had two difficulties to contend with. The first has been the shock resulting from the operation. This is dependent upon the extent of the operation, and must always be a part of a surgical operation. The second has been secondary effects following the operation. After the operation, even though it was successful, there were almost sure to arise secondary complications known as surgical fever, inflammation, blood poisoning, gangrene, etc., which frequently resulted fatally. These secondary complications were commonly much more serious than the shock of the operation, and it used to be the common occurrence for the patient to recover entirely from the shock, but yield to the fevers which followed. They appeared to be entirely unavoidable, and were indeed regarded as necessary parts of the healing of the wound. Too frequently it appeared that the greater the care taken with the patient the more likely he was to suffer from some of these troubles. The soldier who was treated on the battlefield and nursed in an improvised field hospital would frequently recover, while the soldier who had the fortune to be taken into the regular hospital, where greater care was possible, succ.u.mbed to hospital gangrene. All these facts were clearly recognised, but the surgeon, through ignorance of their cause, was helpless in the presence of these inflammatory troubles, and felt it always necessary to take them into consideration.
The demonstration that putrefaction and decay were caused by bacteria, and the early proof that the silkworm disease was produced by a micro-organism, led to the suggestion that the inflammatory diseases accompanying wounds were similarly caused.
There are many striking similarities between these troubles and putrefaction, and the suggestion was an obvious one. At first, however, and for quite a number of years, it was impossible to demonstrate the theory by finding the distinct species of micro- organisms which produced the troubles. We have already seen that there are several different species of bacteria which are a.s.sociated with this general cla.s.s of diseases, but that no specific one has any particular relation to a definite type of inflammation. This fact made discoveries in this connection a slow matter from the microscopical standpoint. But long before this demonstration was finally reached the theory had received practical application in the form of what has developed into antiseptic or aseptic surgery.
Antiseptic surgery is based simply upon the attempt to prevent the entrance of bacteria into the surgical wound. It is a.s.sumed that if these organisms are kept from the wound the healing will take place without the secondary fevers and inflammations which occur if they do get a chance to grow in the wound. The theory met with decided opposition at first, but acc.u.mulating facts demonstrated its value, and to-day its methods have been adopted everywhere in the civilized world. As the evidence has been acc.u.mulating, surgeons have learned many important facts, foremost among which is a knowledge of the common sources from which the infection of wounds occurs. At first it was thought that the air was the great source of infection, but the air bacteria have been found to be usually harmless. It has appeared that the more common sources are the surgeon"s instruments, or his hands, or the clothing or sponges which are allowed to come in contact with the wounds. It has also appeared that the bacteria which produce this cla.s.s of troubles are common species, existing everywhere and universally present around the body, clinging to the clothing or skin, and always on hand to enter the wound if occasion offers. They are always present, but commonly harmless. They are not foreign invaders like the more violent pathogenic species, such as those of Asiatic cholera, but may be compared to domestic enemies at hand. It is these ever-present bacteria which the surgeon must guard against. The methods by which he does this need not detain us here. They consist essentially in bacteriological cleanliness.
The operation is performed with sterilized instruments under most exacting conditions of cleanliness.
The result has been a complete revolution in surgery. As the methods have become better understood and more thoroughly adopted, the instances of secondary troubles following surgical wounds have become less and less frequent until they have practically disappeared in all simple cases. To-day the surgeon recognises that when inflammatory troubles of this sort follow simple surgical wounds it is a testimony to his carelessness. The skilful surgeon has learned that with the precautions which he is able to take to-day he has to fear only the direct effect of the shock of the wound and its subsequent direct influence; but secondary surgical fevers, blood poisoning, and surgical gangrene need not be taken into consideration at all. Indeed, the modern surgeon hardly knows what surgical gangrene is, and bacteriologists have had practically no chance to study it. Secondary infections have largely disappeared, and the surgeon is concerned simply with the effect of the wound itself, and the power of the body to withstand the shock and subsequently heal the wound.
With these secondary troubles no longer to disturb him, the surgeon has become more and more bold. Operations formerly not dreamed of are now performed without hesitation. In former years an operation which opened the abdominal cavity was not thought possible, or at least it was so nearly certain to result fatally that it was resorted to only on the last extremity; while to-day such operations are hardly regarded as serious. Even brain surgery is becoming more and more common. Possibly our surgeons are pa.s.sing too far to the other extreme, and, feeling their power of performing so many operations without inconvenience or danger, they are using the knife in cases where it would be better to leave Nature to herself for her own healing. But, be this as it may, it is impossible to estimate the amount of suffering prevented and the number of lives saved by the mastery of the secondary inflammatory troubles which used to follow surgical wounds.
Preventive medicine, then, has for its object the prevention rather than the cure of disease. By showing the causes of disease and telling us where and how they are contracted, it is telling us how they may to a large extent be avoided. Unlike practical medicine, this subject is one which has a direct relation to the general public. While it may be best that the knowledge of curative methods be confined largely to the medical profession, it is eminently desirable that a knowledge of all the facts bearing upon preventive medicine should be distributed as widely as possible. One person can not satisfactorily apply his knowledge of preventive medicine, if his neighbour is ignorant of or careless of the facts. We can not hope to achieve the possibilities lying along this line until there is a very wide distribution of knowledge. Every epidemic that sweeps through our communities is a testimony to the crying need of education in regard to such simple facts as the source of infectious material, the methods of its distribution, and the means of rendering it harmless.
PREVENTION IN INOCULATION.
It has long been recognised that in most cases recovery from one attack of a contagious disease renders an individual more or less immune against a second attack. It is unusual for an individual to have the same contagious disease twice. This belief is certainly based upon fact, although the immunity thus acquired is subject to wide variations. There are some diseases in which there is little reason for thinking that any immunity is acquired, as in the case of tuberculosis, while there are others in which the immunity is very great and very lasting, as in the case of scarlet fever.
Moreover, the immunity differs with individuals. While some persons appear to acquire a lasting immunity by recovery from a single attack, others will yield to a second attack very readily.
But in spite of this the fact of such acquired immunity is beyond question. Apparently all infectious diseases from which a real recovery takes place are followed by a certain amount of protection from a second attack; but with some diseases the immunity is very fleeting, while with others it is more lasting.
Diseases which produce a general infection of the whole system are, as a rule, more likely to give rise to a lasting immunity than those which affect only small parts. Tuberculosis, which, as already noticed, is commonly quite localized in the body, has little power of conveying immunity, while a disease like scarlet fever, which affects the whole system, conveys a more lasting protection.
Such immunity has long been known, and in the earlier years was sometimes voluntarily acquired; even to-day we find some individuals making use of the principle. It appears that a mild attack of such diseases produces immunity equally well with a severe attack, and acting upon this fact mothers have not infrequently intentionally exposed their children to certain diseases at seasons when they are mild, in order to have the disease "over with" and their children protected in the future.
Even the more severe diseases have at times been thus voluntarily acquired. In China it has sometimes been the custom thus to acquire smallpox. Such methods are decidedly heroic, and of course to be heartily condemned. But the principle that a mild type of the disease conveys protection has been made use of in a more logical and defensible way.
The first instance of this principle was in vaccination against smallpox, now practised for more than a century. Cowpox is doubtless closely related to smallpox, and an attack of the former conveys a certain amount of protection against the latter. It was easy, therefore, to inoculate man with some of the infectious material from cowpox, and thus give him some protection against the more serious smallpox. This was a purely empirical discovery, and vaccination was practised long before the principle underlying it was understood, and long before the germ nature of disease was recognised. The principle was revived again, however, by Pasteur, and this time with a logical thought as to its value. While working upon anthrax among animals, he learned that here, as in other diseases, recovery, when it occurred, conveyed immunity.
This led him to ask if it were not possible to devise a method of giving to animals a mild form of the disease and thus protect them from the more severe type. The problem of giving a mild type of this extraordinarily severe disease was not an easy one. It could not be done, of course, by inoculating the animals with a small number of the bacteria, for their power of multiplication would soon make them indefinitely numerous. It was necessary in some way to diminish their violence. Pasteur succeeded in doing this by causing them to grow in culture fluids for a time at a high temperature. This treatment diminished their violence so much that they could be inoculated into cattle, where they produced only the mildest type of indisposition, from which the animals speedily recovered. But even this mild type of the disease was triumphantly demonstrated to protect the animals from the most severe form of anthrax. The discovery was naturally hailed as a most remarkable one, and one which promised great things in the future. If it was thus possible, by direct laboratory methods, to find a means of inoculating against a serious disease like anthrax, why could not the same principle be applied to human diseases? The enthusiasts began at once to look forward to a time when all diseases should be thus conquered.