DISTRIBUTION AND HABITAT OF THE BACTERIA. 711 



much more suitable for such a multiplication ; what the 

 soil really effects in a marked manner, viz., the preserva- 

 tion and the distribution of the preserved pathogenic 

 agents, is, however, not an exclusive privilege of the soil ; 

 on the contrary, the distribution of these infective agents 

 can also take place by other means and in other ways, 

 which are for the most part more available than the 

 roundabout way through the soil. 



Further, the occurrence of local and seasonal varia- The local and 

 tions in the distribution of the infective diseases, which, predisposition 



according to Pettenkofer, are only explicable on the as- is n j> 

 sumption that the soil exerts an influence, does not by means of the 

 any means necessitate the idea of a constant connection Bother wa S ys 

 between soil and epidemics. We see, on the contrary, 

 that the other modes of spread in which the soil does 

 not come into question, e.g., the spread by the food, by 

 contact, &c., are subject to local and seasonal variations 

 which are quite sufficient to explain the corresponding 

 oscillations of the epidemics (see the following part). 



Bacteria are almost- always present in very varying Occurrence of 

 numbers in water. The varieties observed are almost ^ c t t e e r na m 

 without exception saprophytes. Among these there are 

 some which are of special interest, because they are able 

 to multiply markedly in the presence of imponderable 

 quantities of the most simple nutritive materials, and at 

 a temperature of 8 to 10 C., and hence they are present 

 in large numbers in the most various kinds of water. 

 These "water bacteria" of which Bolton* has isolated six Bacteria 

 varieties, which are very widely distributed, influence the ^Stiply in 

 total number of bacteria in any particular water ; for water - 

 where they are present they multiply with such extreme 

 rapidity, that very soon the number of all the other 

 bacteria becomes insignificant compared with them. The 

 quality of the water is quite indifferent for these typical 

 inhabitants of the water; they multiply quite as markedly 



* Bolton, Ztiitschr. f. Hygiene, vol. i., Part 1. See Cramer, Die Was- 

 servtrsorgung von Zurich. Zurich, 1885. Wolffhiigel, Arb. a. d. Kais. 

 Ges. Amt., 1885, vol. i. Wolffhiigel and Eiedel, ibid., 1886, vol. 2. 

 ieone, Atti cklla R. Acad. del Lincei, Sar. 4, vol. i. 



