the general health; saturation of the soil and of the surrounding media with animal refuse; abundance of body vermin of all kinds, as well as of other vermin, such as rats and mice, which serve as multipliers of the virus; carelessness about personal cleanliness, about wounds of the hands and feet, about clothing, and about food, dishes, and water. One can understand how in such circumstances the germ has opportunities to multiply and spread.
Except in the case of the relatively rare pneumonic form, plague, though " catching," is not nearly so contagious as are scarlet fever, measles, or small-pox. Medical men, and even nurses, in clean airy hospitals rarely contract the disease, provided they have no open wounds and do not remain too long in close proximity to their patients. In cities the cleanly districts are generally spared. This was well exemplified in the recent epidemics at Canton and Hong Kong, where the airy, cleanly European quarters and the relatively clean, well-ventilated boat population were practically exempt, whilst the disease ran riot in the adjoining filthy, overcrowded native houses only a few yards away.
The fact that plague can be communicated to the lower animals by feeding them on the tissues of plague patients and on cultures of the specific bacillus, suggests that the disease may be conveyed to man in food or drink. The bacillus is sometimes found in the intestinal contents of patients. It is also to be found in the urine. Water or food contaminated with sewage or fæcal matter may therefore be regarded as a possible medium of infection. Food contaminated by infected rats is likely also to be a source of danger. In the epidemic of 1902, in Hong Kong, plague bacilli were found in the intestinal contents and mucus of the mouth in about one-third of the plague-infected rats examined, and in the urine in about one-fifth of the cases (Simpson).
The bacilli do not, as a rule, penetrate the unbroken epidermis, as proved by the impunity with which post-mortem examinations in plague cases have often been made; but it seems not improbable that
