of the most widely distributed, most frequent, and most destructive of pestilences" (Hirsch).
The disease was introduced to the West Indies and to Mexico at an early date after the discovery of the "western world," and nearly every fresh outbreak during the sixteenth and seventeenth centuries can be traced to importation from Africa by ships engaged in the slave trade. The entire native population, not having previously been exposed to the ravages of this disease, was susceptible to infection, and "it was so disastrous that whole tribes were exterminated by it. . . . The disease reached Mexico for the first time in 1520 with troops from Spain; the number of persons swept off in a short time has been estimated at three millions and a half "(Hirsch). The disease was first introduced into one of our Atlantic seaports about the middle of the seventeenth century, when it prevailed in Boston. Since that date numerous localized epidemics of greater or less extent have occurred in various parts of the United States, but, owing to the early adoption of the practice of vaccination, it has not obtained a wide diffusion among the white population. It has, however, been very destructive to the aboriginal inhabitants of the country.
We must now turn to the second group of infectious diseases, viz., those in which the specific germ may multiply, under favorable conditions as to climate and soil, external to the bodies of infected individuals, and which have consequently a more or less well-defined geographic range.
In the case of typhoid fever and of the malarial fevers, which belong to this group, the geographic range is very extensive, while in cholera, in yellow fever, and beriberi it is more limited, as will be seen when I come to speak of these several diseases. The specific germ of typhoid fever is now well known, it having been first observed by the German physician Eberth, and independently by the celebrated German bacteriologist Koch, in the year 1880. Its causal relation to the disease was not established until some years later, but is now generally recognized by pathologists and well-informed physicians. This germ is found in the ulcerated glands of the intestine and consequently in the intestinal contents. The discharges from the bowels of typhoid patients, therefore, contain the germs of the disease, which probably multiply indefinitely if they find their way to shallow wells or streams at a season of the year favorable for such development. At all events, whether active development occurs or not, it is well established that typhoid fever is usually contracted by drinking water contaminated by the discharges of typhoid patients. To discuss the relations of this disease to season, temperature, latitude, local insanitary conditions, etc.,
