To Schäffer we owe the discovery that leprosy bacilli may be disseminated in immense numbers by the coughing of leprosy patients, whilst it has been estimated that a tuberculous invalid may discharge a billion tubercle bacilli in the space of twenty-four hours, whilst the dried sputum of consumptive persons has actually engendered tuberculous symptoms in the lungs of animals which were made to inhale it. Plague bacilli have been found in masses in the mouths of plague patients, and were found, moreover, before any symptoms of the disease had declared themselves; and the sputum of infected persons is regarded by some authorities as one of the most important vehicles by which plague is spread. The culpability of air in the dissemination of tuberculosis amongst animals has been made the subject of some very exhaustive and valuable investigations by Kasselmann. In as many as 71 per cent of bovine tuberculosis cases the respiratory organs, Kasselmann found, were the seat of the disease. The undoubted contamination of the air which takes place in the surroundings of tuberculous animals is not, however, due to the bacilli being exhaled by such cattle in the mere process of respiration, for it has been repeatedly found by various investigators that the air expired by infected animals is free from the dreaded tubercle bacteria. As in man, so in animals--it is by the act of coughing that tuberculous secretions are discharged through the mouth and nasal passages, some of which in the form of spray may enable the bacilli to remain suspended in the air for periods of five hours or more, whilst other portions of such secretions fall on the ground or in the feeding troughs, and later on, as dust, may again relentlessly claim their toll of victims. In other cases of tuberculosis the excrementitious matter becomes, of course, a fertile source of infection to the surroundings. The dire results which may follow the introduction of a single tuberculous animal into a healthy stall of cows may be realised from the fact that in one instance a whole herd of twenty-eight animals became in the course of one year infected in consequence of the admission of one diseased cow, the cow-house having previously had a perfectly clean bill of health in this respect. On the Continent the risk of wholesale infection by such means is greater than in this country; for abroad the animals are to a much greater extent stall-fed, and kept shut up both winter and summer. A case is mentioned by the well-known veterinary authority, M. Nocard, of a whole stall of animals becoming infected through the cow-man who tended them being consumptive. He slept in a loft over the cows, and his tuberculous sputum in the form of dust was conveyed to the stalls beneath and so spread the infection.