DETECTION OF PATHOGENIC BACTERIA IN WATER 279 



exclude the possibility of such forms being confounded 

 with the cholera bacillus. Koch states that nearly a 

 dozen such spirillar forms have been isolated in his 

 laboratorjT- from various waters, but that the absence of 

 the indol-reactio7i as well as the absence of any patho- 

 genic effects on guinea-pigs sufficiently distinguished 

 them from the cholera bacillus. In the tables at the 

 end of the book, on pp. 399-408, will be found a 

 description of some of the comma-shaped bacteria 

 isolated by diiferent observers from waters. 



Arens ^ has devised a method by means of which 

 he says that cholera bacilli, even when present in very 

 small numbers (two in 5 c.c. of water), may be with 

 certainty detected. This consists in first rendering the 

 water distinctly alkaline by the addition of l-l'&c.c. 

 of a 10 per cent, solution of caustic potash to 200 c.c. 

 of the water under examination, so that the latter con- 

 tains -OS-'OS per cent, of KOH. This alkalised water 

 then receives pancreas-bouillon in the proportion of one 

 to nine parts of the water. The pancreas-bouillon is 

 composed of broth obtained from the pancreas, to which 

 Witte's peptone is added, and the whole neutralised with 

 carbonate of soda until a highly diluted portion yields 

 a faint red colour with rosolic acid. The treated 

 samples of water are then incubated as in Schottelius' 

 method, and the cholera bacilli are found on the surface 

 of the liquid and may be easily isolated subsequently by 

 means of plate-cultures. 



Sanarelli,^ in his investigations on the presence of 

 spirillar forms in the rivers Seine and Marne and in drain 

 water, adopted the following method for their isolation. 



^ ' Ueber den Nacliweis weniger Cholerakeime in grosseren Mengen 

 Trinkwassers,' MilncJiener med. Wochenschrift, 1893, No. 10. 



^ * Les yibrions des eaux et I'Etiologie du Cholera,' Annates de VInsti- 

 tut Pasteur, vol. vii., 1893, p. 693. 



