The intestinal surface is the most important of these channels, as the writer has endeavoured to prove in the Cavendish Lecture (British Medical Journal, July 11, 1908). Space does not permit of a repetition of the experimental results obtained by the conjoint research carried out by Professor Symmers and himself; suffice it to say that by introducing large doses of living bacilli into the stomach of guinea-pigs by the oeso phageal tube the micro-organisms were found to have penetrated the intact intestinal surface and a few hours afterwards were demonstrated in the lung tissue of the animal. Solid carbon particles, when administered in a similar mariner alone or mixed with tubercle bacilli, were likewise found in the lung tissue, having passed through thelarge-meshed reticulum of the mesenteric glands (without discolouring these organs), to be filtered out of the blood by the fine pulmonary capillaries. These results demonstrate the possibility of the production of pulmonary phthisis through the gastro-intestinal surface without any intestinal or abdominal lesion, as erroneously denied by Koch, especially if we leave out the question of the type of bacillus.
Calmette has demonstrated that when the bacilli are introduced into the stomach of the guinea-pig the cervical lymphatic glands become also involved, thus showing that the theory of the tonsillar route does not always hold true.
When the universally recognised prevalence of tuberculosis in cattle is kept in mind, the bearing of the above facts on prophylaxis becomes obvious. Milk from tuberculous cows, rich in the presence of the infective bacilli, especially when the udder is involved in the disease, supplies the ideal conditions for charging the human organism with large doses of the specific micro-organism, and it must be accepted as proven that the invasion by this route may eventuate in a primary acute general tuber culosis in which the lung suffers with the lymphatic glands of the entire body, though there may be no intestinal ulcers found after death.
Milk, therefore, as an article of food, should be obtained from cows which have been demonstrated to be free from tubercle by testing with tuberculin injections, otherwise it should be sterilised by a heat sufficient to destroy the bacilli. It is the firm conviction of the writer that when uncooked milk becomes recognised (as it should be) to be more dangerous than raw pork then human tuberculosis will become a comparatively rare disease. One more pathological consideration bearing upon the pre vention of phthisis and abdominal tuberculosis must be kept in mind by the physician who tries to guard his patients against tubercular invasion: Von Behring maintained that the phthisis of adults was due to the tardy evolution of intestinal tuberculosis contracted during the early years of life from infected milk, and Vansteenberghe and Grysez claim to have proved experimentally that the tubercle bacillus when injected into the stomach of the very young guinea-pig is filtered out after entering the lacteals by the fine reticulum of the mesenteric glands, which acts at this stage of the animal's existence as an effective barrier to the further entrance of the micro-organisms, and the results of Calmette and Guerin's experiments on young goats prove the same; no involvement of the lungs occurred till after the abdominal glands had caseated. These facts
demonstrate the importance of sterilising all milk employed in infant feeding as well as the milk used as food in childhood and adult life. Under Lymphadenitis the experience of the writer is detailed in which upon a large experimental scale he has conclusively satisfied himself that scrofula may be stamped out by this means.
The important question of infection from breathing the air contaminated by the dried, dust-laden sputum from phthisical patients remains to be considered. Whether the bacilli directly gain an entrance into the air cells in this manner (as denied by Calmette and his disciples), or whether they reach the lung after being swallowed with the saliva and enter the pulmonary substance through the lacteals, is probably only a problem of academic interest. Whilst it would be unwarrantable to conclude in either case that phthisis cannot be produced in this manner it is obvious that the risk, the important question of dosage being considered, is much less than in the case of the ingestion of uncooked tuberculous milk. Hence, whilst ordinary wisdom would suggest the advisability of destroy ing all sputum as it is expectorated, and of avoiding close intercourse of the phthisical with the healthy, these precautions should never be per mitted to interfere with a rigorous surveillance of the milk supply.
The physician should recognise the fact that in the case of even advanced tuberculosis in cattle the animals often present none of the ordinary signs invariably present in phthisical patients. The condition of the animal may appear to be normal, and even a large amount of adipose tissue may be obviously present with a shining coat and a capacity for the production of a large amount of apparently healthy milk, though the internal organs and the mammary glands may he studded with tubercles and the milk laden with bacilli.