298 POPULAR SCIENCE MONTHLY. 



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 pre- 

 viously been exposed to the ravages of this disease, was susceptible 

 to infection, and " it was so disastrous that whole tribes were exter- 

 minated 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 pre- 

 vailed 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 ob- 

 served 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 dis- 

 charges of typhoid patients. To discuss the relations of this disease 

 to season, temperature, latitude, local insanitary conditions, etc., 



