Upon reflection it will at once be seen that from these experimental data showing the ready penetrability of the infantile mucous membrane, another logical deduction follows: If even non-virulent anthrax bacilli introduced per stomach gain ready access to the circulation of the new-born, then it must be possible for all the bacteria of milk to do the same, and we may therefore expect that the accidental presence of pathogenic bacteria in the milk fed to infants will exercise a damaging influence on the infant organism. In considering their pathogenic possibilities the amount of the infectious germs which enter the system must, of course, be a matter of some importance. Under certain conditions, however, even a few germs may be sufficient to excite disease, for in the intestines, especially in the cæcum, they find an excellent place of incubation where they can multiply. A milk very poor in disease germs may thus lead to a virulent infection. In breast-fed infants the danger of introducing disease germs, excepting tubercle bacilli, of which I shall speak later, is not very great, for it is very unusual for living germs derived from the interior of the body to appear in the milk. The germs which can be found, even in perfectly fresh milk, are derived from the surface of the body, or from the mouths of the lacteals, or possibly even from the glandular epithelium, as researches conducted by myself, assisted by Mr. Rösler, have shown.
But in artificially nourished infants the matter is altogether different. It would be a miracle if, after all the manipulations to which the milk supplied to our large cities is subjected, it did not occasionally contain disease germs derived from the milker or from other persons who have handled the milk.
If, by the time the milk reaches the city, the proliferation of these pathogenic micro-organisms has already gone on to a considerable extent, then usually the milk will contain a number of poisonous substances in addition to the micro-organisms. Some of these germs are killed by the scalding to which the milk is usually subjected before feeding, and the virulence of the rest is much diminished, so that in boiled milk practically no danger is to be apprehended from the micro-organisms. We are not at all sure, however, that we have made the toxins innocuous by this boiling, and probably a great many cases of intestinal catarrh in artificially nourished children are due, not to a parasitic, but to a toxic infection.
I said it would be a miracle if artificially nourished infants did not frequently suffer from milk infections, and I can add that this miracle does not, in fact, occur. One need only glance at the mortality statistics of artificially nourished infants in order to realize that my experimental results absolutely agree with the facts. The following figures are taken from the excellent report, “Gesundheitswesen des preussischen Staates im Jahre 1901,” which has recently been published by the Prussian government.
In the city of Stettin, the mortality for the first year of life was 473.52 for every 1000 living children of the same age; whereas in the period of 10 to 15 years the mortality was 2.94 to each 1000 living children of that age. In other words, during the same length of time 161 times as many infants up to one year died as did children over ten years.
Berlin, with a mortality of 286.29⁰⁄₀₀ for the first year of life, stands about midway in the list of Prussian cities having over 100,000 population. Cassel, with 183.54⁰⁄₀₀, shows about the lowest figure, and even this is inordinately high, for it is not in the nature of things that this is so. We are not facing a necessity of nature to which we must submit like fatalists. This can be readily seen by observing that there are towns and whole regions in which the mortality figures for the first year are kept within moderate limits. In Ireland and Scotland, as well as in Norway and Sweden, the mortality for this period scarcely exceeds 10⁰⁄₀₀, about one-fiftieth the mortality in Stettin. In Stockholm I visited a foundling asylum with an organization bound to excite admiration and wonder, in which, as I recollect, the mortality was still less.
Nowadays the assertion that the character of the milk fed to infants is responsible for the great differences in the mortality statistics is nowhere seriously questioned. There are, however, wide differences of opinion as to what the determining factors are, and how, in places where the mortality figures are so outrageously high, we can remedy the evil.
According to my researches into this subject this problem will not be successfully solved by the efforts now being made to secure the use of sterilized milk. I am, in fact, in doubt whether milk sterilization as at present practised can much longer pass as a hygienic measure. For the present, to be sure, we have nothing better. But the discussion of this question does not fall within the scope of this lecture. I have quoted the statistics of the high infant mortality in our large cities merely in order to advance a further epidemiological argument for my assertion that the infant alimentary tract is defenseless against infectious agents whether these are living or not. Even the infectious toxins pass unchanged through the intestinal mucous membrane of very young individuals, though not through that of healthy older ones. A real advance in milk hygiene can, however, be begun even now if the milk be pasteurized at the dairies and not at the large receiving-stations in the cities. In the raising of calves, this procedure has proven of great value.
I have made exhaustive studies to discover why the intestinal mucous membrane of the young should offer so little resistance to the passage of corpuscular infectious substances. I shall content myself here with the statement that the mucous membrane of new-born individuals possesses no continuous epithelial covering and that the gland-tubes of the ferment-producing glands are little, if at all, developed at this time.
By having thus presented to you the results of my experiments and explained my epidemiological views, I have not really deviated from the subject of the suppression of tuberculosis. We have seen that the tubercle bacilli which gain access to the system through the alimentary tract in infancy constitute the important etiological factor in the production of the tubercular infection which leads to consumption, and I believe that the realization of this great fact will supply us with a rational plan for combating tuberculosis. It will be necessary to strive more than ever to secure a suitable milk diet for new-born and very young children, one based on sound experimental investigations. The as yet unsolved problem, that of a rational milk hygiene in the suppression of tuberculosis, coincides with the problem of milk-feeding of infants in general. The mode of infection is everywhere the same, but the infectious agents are of great variety. Most of them excite acute diseases which end either fatally or in entire recovery; in the latter case with a simultaneous development of immunity. The virus of tuberculosis, however, behaves quite differently, creeping in most insidiously, all unnoticed, and being in this respect analogous only to the virus of leprosy, of syphilis, or possibly of malaria in tropical countries. It may be months, years, or decades before the infection leads to manifest disease. This depends on the virulence of the virus, which is generally much greater in the virus of bovine tuberculosis than in that of human tuberculosis. It also depends on the number of bacilli introduced per stomach, and whether such introduction is single or oft repeated. In the human being months and years may elapse before the infection is followed by any sensitiveness to tuberculin injections in the usual dose. If, then, at the time of puberty, or after an exhausting puerperium, after too great a demand on the milk secretion (especially with insufficient food), after so-called colds and other unfavorable meteorological conditions, after muscular over-exertion, under conditions unfavorable to life, such as improper nourishment, confinement in insufficiently or badly ventilated rooms, etc., if, after any of these, pulmonary disease develops whose tubercular nature we cannot doubt, then we are dealing with the beginning of consumption; the beginning of tubercular lesions is much further back; and the first introduction of the disease germs, in other words, the beginning of the infection, is far back in earliest infancy. This must be so, for we see many individuals, though subject to the most unfavorable conditions, for example, those confined in unsanitary prisons, wholly escape tuberculosis.