THE MICROBES OF WATER 297 



river if its volume is not more than -j^th that of 

 the river water and its rate of flow decidedly greater 

 than that of the current ; and it has been shown 

 that the Isar, for example, possesses this self- 

 purification. The bacteriological investigations of 

 Prausnitz prove the purifying power of the Isar. 

 The number of 198,000 microbes per cc. found at 

 the mouth of the Munich sewer was reduced at 

 Ismaning to 15,231, and at Freisingto 3602. These 

 results agree with those of other bacteriologists. 

 Fraenkel found in the water of the Spree above and 

 below Berlin 6000 microbes per cc., but in the city 

 a million. It has been stated that ' the mere number 

 of microbes found has, however, no sanitary signifi- 

 cance, since the microbes found in the water are 

 almost exclusively harmless, and, indeed, destroy the 

 pathogenic microbes in the struggle for existence.' 

 But it should not be forgotten that Griiber 1 and 

 Frankland 2 have shown that Spirillum cholerce 

 Asiaticce, Bacillus anthracis, etc., are capable of living 

 and multiplying in sewage, and that the first-named 

 microbe retained its vitality for 1 1 months ' in com- 

 pany with countless numbers of a micrococcus which 

 had accidentally gained access.' 



' It is necessary, therefore, to exercise considerable 

 caution in judging upon this point in the present 

 state of our knowledge, and it would be highly pre- 

 mature to place too much reliance upon this alleged ./ 

 destruction of pathogenic forms by non-pathogenic 



1 Wiener Medicinische Wochemchrift, 1887. 



2 Proceedings of Royal Society, 1886 ; and Journ. Society of 

 Chemical Industry, vol. vi. (1887). 



