_C._ =Lungs.=--The varied types of pneumonia due to many different organisms (tubercle, glanders, influenza, plague bacilli, pneumococcus, streptococcus, micrococcus and many others) show how frequently these organs are the seat of a localized infection, which may or may not be general. Whether the lungs are the actual point of entrance in these cases is a question which is much discussed at the present time, particularly with reference to tuberculosis. The mucous secretion of the respiratory tract tends to catch incoming bacteria and other small particles and the ciliary movement along bronchial tubes and trachea tends to carry such material out. “Foreign body pneumonia” shows clinically, and many observers have shown experimentally that microörganisms may reach the alveoli even though the exchange of air between them and the bronchioles and larger bronchi takes place ordinarily only by diffusion. The presence of carbon particles in the walls of the alveoli in older animals and human beings and in those that breathe dusty air for long periods indicates strongly, though it does not prove absolutely, that these came in with inspired air. On the other hand, experiment has shown that tubercle bacilli introduced into the intestine may appear in the lungs and cause disease there and not in the intestine. It is probably safe to assume that in those diseases which are transmitted most readily through close association though not necessarily actual contact, the commonest path is through the respiratory tract, which may or may not show lesions (smallpox, scarlet fever, measles, chicken-pox, whooping-cough, pneumonic plague in man, lobar and bronchopneumonias and influenza in man and animals, some cases of glanders and tuberculosis). On the other hand, the fact that the _Bacterium typhosum_ and _Bacterium coli_ may cause pneumonia when they evidently have reached the lung from the intestinal tract, and the experimental evidence of lung tuberculosis above mentioned show that this route cannot be excluded in inflammations of the lung. _D._ =Alimentary Tract.=--The alimentary tract affords the ordinary path of entrance for the causal microbes of many of the diseases of animals and man, since they are carried into the body most commonly and most abundantly in the food and drink. (_a_) The stomach is rarely the seat of local infection, even in ruminants, except as the result of trauma. The character of the epithelium in the rumen, reticulum and omasum in ruminants, the hydrochloric acid in the abomasum and in the stomachs of animals generally are usually sufficient protection. Occasionally anthrax “pustules” develop in the gastric mucosa. (The author saw nine such pustules in a case of anthrax in a man.)