HYGIENE OF MILK AND MEAT. SANITARY POLICE MEASURES.
This has a reference to both man and beast and involves measures of private and public hygiene alike. In man, as we have seen, milk is the source of greatest danger, being habitually taken uncooked, whereas meat has been usually subjected to a high temperature before it comes to the table.
Milk. The unsterilized milk of the tuberculous cow must always be regarded with grave suspicion. Especially is the drinking of milk warm from the cow to be strongly condemned. The feeding experiments of Vilemin, Gerlach and others, in 1866 to 1869, demonstrated the virulence on the lower animals of the milk of infected cows, and many accidental infections have shown the same for man. (See relation of the bacillus of man to that of animals). This conceded, the question arose as to the virulence of milk drawn from the sound udders of tuberculous cows. Many experiments of Nocard, Galtier, McFadyean and others seemed to decide against such infection. Others have had a different experience, and especially when the test was made by inoculation. Ernst found tubercle in 30 per cent. of the cows he examined, though no affection of the udder could be made out. Theobald Smith, Hirschberger, Bang and others found tubercle bacilli in milk from sound udders. Pearson, injecting the milk from sound udders intraperitoneally into Guinea pigs had ten in sixty-three affected. Rabinowitsch and Kemper found tubercle bacilli in ten out of fifteen cows with sound udders. While it must be allowed that often a very small proportion of tuberculous cows with sound udders pass the bacilli in the milk yet a sufficient number of exceptions are found to deter one from endorsing such milk as safe. Much more is this conclusion justified by the consideration that commencing mammary tuberculosis is in many cases unrecognizable by ordinary examination intravitam or post mortem. Again when the bacilli are circulating in the blood (generalized tuberculosis) they can escape from such a vascular tissue as the mamma without the formation of a local lesion, as they can pass through the intestinal walls or lungs and colonize the adjacent lymph glands. Nocard’s injections of the bacilli into the veins seem to show that they disappear from the blood in 4 to 6 days, but with a generalization of the infection from within, the presumption is against a single isolated entrance of bacilli, and in favor of a continuous introduction. In such generalization therefore the bacilli circulate in all vascular tissues, and are liable to escape with any normal secretion, but especially with the milk or urine on account of the great vascularity of the glands.
When the udder is itself tuberculous the case is incomparably worse. The milk can scarcely fail to be infecting, and the bacilli, grown in these highly vascular tissues, apart from the air, are usually of a very virulent type. Of these Martin writes in the report of the Royal Commission (England): “The milk of cows with tuberculosis of the udder possesses a virulence which can only be described as extraordinary. All animals inoculated showed tuberculosis in its most rapid form.” Woodhead is equally positive in this position. Galtier says “we should absolutely avoid the consumption of milk from cows in which the udder is tuberculous, and boil before using, the milk of all cows affected with, or suspected of tuberculosis in any form.” Finally we should never consume without boiling, milk of which we do not certainly know the origin, and especially in cities, we ought not to omit this precaution in the case of milk furnished by milkmen.” Rabinowitsch and Kemper add: “Milk from cows that react to tuberculin must be suspected of being tuberculous in every case.”
It may well be allowed that the mixed milk from a large dairy, containing but one or two tuberculous cows, is much less infecting than that of the tubercular cow herself, and that skim milk that has been passed through the separator has been robbed of many bacilli which have been precipitated in the albuminoid material that collects on the inner side of the bowl. But these mean dilution not purification: they reduce the danger but do not altogether remove it, and sanitary police should aim at sterilization in every case where available.
Butter, cheese, whey, and other dairy products have been proved virulent in different cases (Galtier, Heim, Lasar, Bang, Obermüller, Roth, Groëning, Gasperimi, Petri, Rabinowitsch). This was true for butter 120 days old, and cheese 330 days. In a number of cases Rabinowitsch found a bacillus, similar to the tubercle bacillus and producing tubercle-like lesions, but differing in its staining, morphology and culture, and she supposed that other observers had mistaken this for the tubercle bacillus. Petri, Morgenroth and Hormann, found the bacillus of Rabinowitsch in company with the real tubercle bacillus in butter, and Rabinowitsch, later, in fifteen samples of butter found the bacillus tuberculosis in two.
Bacilli coming from the mouth, bowels, or lungs, are also liable to get into the milk, through the floating dust of the stable, or from the teats, udder, tail, etc., (Gaffky).
Oleomargarine cannot be considered as free from this indictment, for though the tuberculous glands, etc., from the mesentery, may be sterilized in the preliminary heating process, yet the subsequent mixing with milk is liable to convey the infection.
The ideal course with milk, if the herds cannot be purified from tuberculosis, would be to compulsorily remove from the herd every cow that shows objective symptoms of tuberculosis, or any internal disease of the udder, and to subject all the milk of the remainder to Pasteurization at a temperature of 155° F. for twenty to thirty minutes. This, however, requires skilled and faithful management to avoid renewed contamination from the lips of the vessel which may have escaped the heat, or from hands, vessels and objects that were in contact with the milk before. The boiling temperature for fifteen minutes would be a safer resort, as requiring less careful handling, yet even this may be contaminated afterward under poor management. It has the further drawback of the boiled milk taste and the coagulation of the albumen. But the outlay for such careful sterilization will soon amount to more than will the tuberculin test.
Meat. For various reasons meat must be held less virulent than milk, but mainly because it is less frequently the seat of tubercle than the udder, and because it is usually cooked before being eaten. The muscular tissue of the ox appears to be unfavorable to colonization by the bacillus, and although the intermuscular lymph glands do not partake of this inherent resistance, yet as the glands are very frequently affected from the tissues which they drain, they necessarily partake in some degree of the comparative immunity of the muscles. This immunity is, however, far from complete, as the frequent implication of the intermuscular glands (prescapular, axillary, prefemoral, etc.), sufficiently show. Again in estimating the virulence of meat we must never forget that in the great majority of cases, in ordinary infected herds, the tubercle is still essentially local; no generalization has taken place. The muscle is vascular throughout, and in cases of generalized tuberculosis is infecting, yet a single transient escape of tubercle bacilli into the blood does not ensure permanent infection of that fluid, which can usually purify itself in six days or less (Nocard). On the contrary, when the escape of bacilli into the blood is constant, so becomes of necessity the virulence of the blood and a rapid generalization ensues. Such continuous escape may occur in actively advancing tuberculosis at any point, but it is more certain if the degenerating tubercle has opened through the walls of the vessels (capillaries), so that the infecting bacilli can pass into the blood in a continuous stream. The pus and other microbes, in complex infections, hasten this degeneration and contribute to generalization of the tubercle and emaciation. The transient infection of the blood with the pure tubercle bacillus does not, however, lead to emaciation and marasmus, and hence the frequency of high condition in spite of extensive tuberculosis.