Part 8 (1/2)

One of the first differences found to exist among these three types of bacteria was the extraordinary variation in their power of attacking different animals. For instance, while the guinea-pig and the rabbit could be readily inoculated with _human_ bacilli, they could only be infected with difficulty by cultures of the _bovine_ bacillus; while the only animal that could be inoculated at all with the _avian_ or bird bacillus was the rabbit, and he only occasionally. In fact, bacteriologists soon came to the consoling conclusion that the _avian_ bacillus might be practically disregarded as a source of danger to human beings, so widely different were the conditions in their moist and moderately warm tissues to those of the dry and superheated tissues of the bird to which it had adjusted itself for so many generations.

And next came the bold p.r.o.nunciamento of no less an authority than Koch himself, that the bovine bacillus also was so feebly infective to human beings that it might be practically disregarded as a source of danger.

This promptly split the bacteriologists of the world into two opposing camps, and started a warfare which is still being waged with great vigor. As the question is still under hot dispute by even the highest authorities, it is, of course, impossible to p.r.o.nounce any definite conclusions. But the net result to date appears to be that while Koch made a serious error of judgment in declaring that meat and milk as a source of danger to human beings of tuberculosis might be disregarded, yet, for practical purposes, his position is, in the main, correct: the actual danger from the bovine bacillus to human beings is relatively small.

There was nothing whatever improbable, in the first place, in the correctness of Koch's position.

It is one of the few consoling facts, well known to all students of comparative pathology or the diseases of the different species of animals, how peculiarly specialized they are in the choice of their diseases, or, perhaps, to put it more accurately, how particular and restricted disease-germs are in their choice of a host. For instance, out of twenty-eight actually infectious diseases which are most common among the domestic animals and man, other than tuberculosis, only one--_rabies_--is readily communicable to more than three species; only three--_anthrax_, _teta.n.u.s_, and _foot-and-mouth disease_--are communicable to two species; while the remainder are almost absolutely confined to one species, even though this be thrown into closest contact with half a dozen others.

Again, we have half a dozen similar instances in the case of tuberculosis itself. The horse and the sheep, for instance, are both most intimately a.s.sociated with cattle, pastured in the same fields, fed upon the same food, and yet tuberculosis is almost unknown in sheep and decidedly uncommon in horses, and when it does occur in them is from a human source. The goat is almost equally immune from both human and _bovine_ forms, while the cat and the dog, although developing the infection with a low degree of frequency, almost invariably trace that infection to a human source.

There is, therefore, no _a priori_ reason whatever why we should be any more susceptible to bovine tuberculosis than the remainder of the domestic animals. It is only fair to say, however, that the animal whose diet--and appet.i.te--most closely resembles ours, the hog, is quite fairly susceptible to bovine tuberculosis if fed upon the milk or meat of tuberculous cattle.

Next came the particularly consoling fact that although nothing has been more striking than the great increase in the amounts of meat and milk consumed by the ma.s.s of the community during our last twenty years'

progress in civilization, this has been accompanied not by any increase of tuberculosis, but by a _diminution of from thirty-five to forty-five per cent_. The allegation so frequently made that there has been an increase in the amount of infantile tuberculosis has been shown, upon careful investigation by Shennan of Edinburgh, Guthrie of London, Kossel in Germany, Comby in France, Bovaird in New York, and others, to be practically without foundation.

Then, while repet.i.tions of Koch's experiment, upon which his announcement was based, of inoculating calves and young cattle with _human_ bacilli have proved that a certain number of them can be, under appropriate circ.u.mstances, made to develop tuberculosis, that number has never been a large percentage of the animals tested, and in many cases the infection has been a local one, or of a mild type, which has resulted in recovery. Lastly, while a number of bacilli, with _bovine_ culture and other characteristics, have been recovered from the bodies of children dying of tuberculosis, and these bacilli have proved virulent to calves when injected into them, yet, as a matter of historical fact, the actual number of instances in which children or other human beings have been definitely proved to have contracted the disease from the milk of a tuberculous cow is still exceedingly and encouragingly small. A careful study of the entire literature of the past twenty years, some three years ago, revealed _only thirty-seven cases_; and of these thirty-seven Koch's careful investigations have since disproved the validity of nine.

On the other hand, it is anything but safe to accept Koch's practical dictum and neglect the meat and milk of cattle as a source of danger in tuberculosis. First, because the degree of our immunity against the bovine bacilli is still far from settled; and, second, because, while bacteriologists are fairly agreed that the _avian_, the _bovine_, and the _human_ represent three distinct and different variations, if not species, of the bacillus, they are almost equally agreed that they are probably the descendants of one common species, which may possibly be a bacillus commonly found upon meadow gra.s.ses, particularly the well-known timothy, and hence very frequently in the excreta of cattle, and known as the _gra.s.s bacillus_ or _dung bacillus_ of M[oe]ller. This bacillus has all the staining, morphological, and even growth characteristics of the tubercle bacillus except that it produces only local irritation and little nodular ma.s.ses, if injected into animals. Our knowledge of its existence is, however, of great practical importance, inasmuch as it warned us that in our earlier studies of the bacilli contained in milk and b.u.t.ter we have been mistaking this organism for a genuine tubercle bacillus. As a consequence, of late years our tests for the presence of tubercle bacilli in milk are made not only by searching for the organism with the microscope, but also by injecting the centrifugated sediment of the infected milk into guinea pigs, to see if it proves infectious. Many of our earlier statements as to the presence of tubercle bacilli in milk and b.u.t.ter are now invalidated on this account.

Not only are the three varieties of tubercle bacilli probably of common origin, but they may, under certain peculiar conditions, be transformed into one another, or, at least, enabled to live under the conditions favorable to one another. This was shown nearly fifteen years ago by the ingenious experiments of Nocard, the great veterinary pathologist. He took a culture of bovine bacilli, which were entirely harmless to fowls, and, inclosing them in a collodion capsule, inserted them into the peritoneal cavity of a hen. The collodion capsule permitted the fluids of the body to enter and provide food for the bacilli, but prevented the admission of the leucocytes to attack and destroy them. After several weeks the capsule was removed, the bacilli found still alive, and transferred to another capsule in another fowl. When this process had been repeated some five or six times, the last generation of bacilli was injected into another fowl, which promptly developed tuberculosis, showing that by gradually exposing the bacilli for successive generations to the high temperature of the bird's body (from five to fifteen degrees above that of the mammal), they had become acclimated, as it were, and capable of developing. So that it is certainly quite conceivable that bovine bacilli introduced in milk or meat might manage to find a haven of refuge or lodgment in some out-of-the-way gland or tissue of the human body, and there avoid destruction for a sufficiently long time to become acclimated and later infect the entire system.

This is the method which several leaders in bacteriology, including Behring (of ant.i.toxin fame), believe to be the princ.i.p.al source and method of infection of the human species. The large majority, however, of bacteriologists and clinicians are of the opinion that ninety per cent of all cases of human tuberculosis are contracted from some human source. So that, while we should on no account slacken our fight against tuberculosis in either cattle or birds, and should encourage in every way veterinarians and breeders to aim for its total destruction,--a consummation which would be well worth all it would cost them, purely upon economic grounds, just as the extermination of human tuberculosis would be to the human race,--yet we need not bear the burden of feeling that the odds against us in the fight for the salvation of our own species are so enormous as they would be, had we no natural protection against infection from animals and birds.

The more carefully we study all causes of tuberculosis in children, the larger and larger percentage of them do we find to be clearly traceable to infection from some member of the family or household. In Berlin, for instance, Kayserling reports that seventy per cent of all cases discovered can be traced to direct infection from some previous human case.

Lastly, what of the left wing of our army of extermination, composed of those light-horse auxiliaries--the general progress and new developments of civilization, and the net results upon the individual of the experiences of his ancestors, which we designate by the term ”heredity”?

For many years we were in serious doubt how far we could depend upon the loyalty of this group of auxiliaries, and many of the faint-hearted among us were inclined to regard their sympathies as really against us rather than with us, and prepared to see them desert to the enemy at any time. It was pointed out, as of great apparent weight, that consumption was decidedly and emphatically a disease of civilization; that it was born of the tendency of men to gather themselves into clans and nations and crowd themselves into villages and those hives of industry called cities; that the percentage of deaths from tuberculosis in any community of a nation or any ward of a city was high in direct proportion to the density of its population; and that the whole tendency of civilization was to increase this concentration, this congestion of ground s.p.a.ce, this piling of room upon room, of story upon story. How could we possibly, in reason, expect that the influences which had caused the disease could help us to cure it?

But the improbable has already happened. Never has there been a more rapid and extraordinary growth of our great cities as contrasted with our rural districts, never has there been a greater concentration of population in restricted areas than during the past thirty-five years.

And yet, the prevalence of tuberculosis in that time, in all civilized countries of the earth, has shown not only no increase, _but a decrease of from thirty-five to fifty per cent_. To-day the world power which has the largest percentage of its inhabitants gathered within the limits of its great cities, England, has the lowest death-rate in the civilized world from tuberculosis, although closely pressed within the last few years by the United States, whose percentage of urban population is almost equally large, while England's sister island, Ireland, with one of the highest percentages of rural and the lowest of urban population, has one of the highest death-rates from tuberculosis, and one which is, unfortunately, increasing.

The real cure for the evils of civilization would appear to be _more civilization_, or, better, perhaps, _higher_ civilization. Nor are these exceptional instances. Take practically any city, state, or province in the civilized world, which has had an adequate system of recording all births and deaths for more than thirty years, and you will find a decrease in the percentage of deaths from tuberculosis in that time of from twenty to forty per cent. The city of New York's death-roll, for instance, from tuberculosis, per one thousand living, is some thirty-five per cent less than it was thirty years ago. So that our fight against the disease is beginning to bear fruit already. As Osler puts it, we run barely half the risk of dying of tuberculosis that our parents did and barely one-fourth of that of our grandparents.

But this gratifying improvement goes deeper, and is even more significant than this. It is, of course, only natural to expect that our vigorous fight against the spread of the infection of the disease would give us definite results. But the interesting feature of the situation is that this diminution in England and in Germany, for instance, began not merely twenty, but thirty, forty, even fifty years ago--two decades before we even knew that tuberculosis was an infectious disease with a contagion that could be fought.

In the case of England, for instance, we have the, at first sight, anomalous and even improbable fact that the rate of decline in the death-rate from tuberculosis for the twenty years preceding the discovery of Koch's bacillus was almost as great as it has been in the twenty years since. In other words, the general tendency, born of civilization, toward sanitary reform, better housing, better drainage, higher wages and consequently more abundant food, rigid inspection of food materials, factory laws, etc., is of itself fighting against and diminis.h.i.+ng the prevalence of the ”great white plague” by improving the resisting power and building up the health of the individual.

Civilization is curing its own ills.

It must be remembered that vital statistics, showing the decrease of a given disease within the past forty or fifty years, probably represent not merely a real decrease of the amount indicated by the figures but an even greater one in fact; because each succeeding decade, as our knowledge of disease and the perfection of our statistical machinery improves and increases, is sure to show a prompter recognition and a more thorough and complete reporting of all cases of the disease occurring. Statistics, for instance, showing a moderate apparent rate of _increase_ of a disease within the last thirty years are looked upon by statisticians as really indicating that it is at a standstill. It is almost certain that at least from ten to twenty per cent more of the cases actually occurring will be recognized during life and reported after death than was possible with our more limited knowledge and less effective methods of registration thirty years ago. So we need not hesitate to encourage ourselves to renewed effort by the reflection that we are enlisted in a winning campaign, one in which the battle-line is already making steady and even rapid progress, and which can have only one termination so long as we retain our courage and our common-sense.

This decline of the tuberculosis death-rate is, of course, only a part of the general improvement of physique which is taking place under civilization. If we could only get out from under the influence of the ”good old times” obsession and open our eyes to see what is going on about us! There is nothing mysterious about it. The soundest of physical grounds for improving health can be seen on every hand. We point with horror, and rightly, to the slum tenement house, but forget that it is a more sanitary human habitation than even the houses of the n.o.bility in the Elizabethan age. We become almost hysterical over the prospect that the very fibre of the race is to be rotted by the adulteration of our food-supply, by oleomargarine in the b.u.t.ter, by boric acid in our canned meats, by glucose in our sugar, and aniline dyes in our candies, but forget that all these things represent extravagant luxuries unheard of upon the tables of any but the n.o.bility until within the past two hundred, and in some cases, one hundred, years. Up to three hundred years ago even the most highly civilized countries of Europe were subject to periodic attacks of famine; our armies and navies were swept and decimated with scurvy, from bad and rotten food-supplies; almost every winter saw epidemics breaking out from the use of half-putrid salted and cured foods; only forty years ago, a careful investigation of one of our most conservative sociologists led him to the conclusion that in Great Britain _thirty per cent of the population never in all their lives had quite as much as they could eat_, and for five months out of the year were never comfortably warm. The invention of steam, with its swift and cheap transportation of food-supplies, putting every part of the earth under tribute for our tables, meat every day instead of once a week for the workingman, and the introduction of sugar in cheap and abundant form, with the development of the dietary in fruits and cereals which this has made possible, have done more to improve the resisting power and build up the physique of the ma.s.s of the population in our civilized communities, than ten centuries of congestion and nerve-worry could do to break it down.

We shake our heads, and prate fatuously that ”there were giants in those days,” ignorant of the thoroughly attested fact, that the average stature of the European races has increased some four inches since the days of the Crusaders, as shown by the fact that the common British soldier of to-day--Mr. Kipling's renowned ”Tommy Atkins,” who is looked upon by the cla.s.ses above him in the social scale as a short, undersized sort of person--can neither fit his chest and shoulders into their armor, get his hands comfortably on the hilts of their famous two-handed swords, nor even lie down in their coffins.

We are at last coming to acknowledge with our lips, although we scarcely dare yet to believe it in our heart of hearts, that not merely the death-rate from tuberculosis, but the general death-rate from all causes in civilized communities, is steadily and constantly declining; that the average longevity has increased nearly ten years within the memory of most of us, chiefly by the enormous reduction in the mortality from infant diseases; and that, though the number of individuals in the community who attain a great or notable age is possibly not increasing, the percentage of those who live out their full, active life, play their man's or woman's part in the world, and leave a group of properly fed, vigorous, well-trained, and educated children behind them to carry on the work of the race, is far greater than ever before. Even in our much-denounced industrial conditions, made possible by the discovery of steam with its machinery and transportation, the gain has far exceeded the loss. While machinery has made the laborer's task more monotonous and more confining, the net result has been that it has shortened his hours and increased his efficiency.