522 THE POPULAR SCIENCE MONTHLY. 



the opposite side of the street L. These three houses contained fifteen 

 inmates, all of them coming into frequent contact with the sick. These 

 people were supplied with water from the well at v, and were through- 

 out the epidemic exempt from the disease. Thus, to sum up, all the 

 families that were supplied from the Schmidt well after the 20th of Sep- 

 tember had one or more m.embers attacked by the fever ; all the fami- 

 lies that were furnished with water from other sources escaped. The 

 conclusion is reasonable that in the drinking-water we have the means 

 of the diffusion of the germs. 



I have here shown a direct connection between the case of Otto 

 Schmidt and that of every other infected person. This connection, 

 traced through the drinking-water, was a discovery in our own epi- 

 demic; but it is by no means a discovery as a means of diffusion of the 

 disease. This has long been known, and the literature of the subject 

 is full of instruction. 



It must be borne in mind, however, that not all water contaminated 

 with organic impurities will cause typhoid fever. There must be among 

 these impurities the specific poison of the disease. And this, as we 

 have been able to prove, can be traced to former foci of typhoid fever. 

 Other fluids may be contaminated in the same manner. An interesting 

 report of an epidemic of the disease in England was given in the " Lan- 

 cet " several years ago. A pasture had been manured by sewer prod- 

 ucts. Here were fed a large number of milch cows. In a neighboring 

 town typhoid fever became rife. The victims, it was discovered, all used 

 milk from this dairy ; those who did not make use of it escaped. One 

 can not help speculating about the way in which the disease-germs en- 

 tered the milk. The more probable explanation is a mechanical one : 

 that the germs adhered to the udders of the cows and were brushed off 

 in the act of milking. It hardly seems reasonable that the germs passed 

 through the organism of the cows and thus entered the milk. The the- 

 ory of a contagium vivum is further fortified by the circumstance that, 

 by boiling, the power to harm is taken away from the infected fluids. 



It must be observed that between the entrance of the infecting ele- 

 ments into the system and the breaking out of the symptoms which 

 define the disease, a varying period of time intervenes. This is called 

 the period of incubation. It is a feature which distinguishes the entire 

 group of infectious diseases. In determining the length of this period 

 there are two elements of uncertainty: first, it is difficult to fix the 

 exact time of infection ; secondly, it is often impossible to define the 

 exact beginning of the disease. In typhoid fever, 'especially, the onset 

 is insidious and slow. Days and even weeks may be passed in a de- 

 pressed, languid state of the health, before the disease is recognized as 

 typhoid fever. Among business men these initial symptoms are often 

 explained by taking cold, or by overwork. During the epidemic at 

 Basle a few persons were attacked after a residence in the city of from 

 seven to fourteen days ; others after sixteen days. Haegler found in 



