308 MICRO-ORGANISMS IN WATER 



As regards the behaviour of the cholera spirilla in 

 unsterilised waters, the criticism which we offered 

 above in connection with the same problem concerning 

 the typhoid bacilli, applies with equal force here, for 

 unless special methods (see p. 276) be adopted for the 

 discovery of the cholera bacilli in unsterilised waters, 

 there can be no doubt that they will in many cases be 

 entirely overlooked. Unfortunately, no such special 

 methods of detection have been employed in the case 

 of any of the experiments recorded above on the 

 cholera bacilli in unsterilised water. The results of 

 these experiments, which must therefore be accepted 

 with considerable reserve, indicate that in unsterilised 

 water the vitality of the cholera spirilla is of the very 

 briefest duration (according to Kraus they had disap- 

 peared on the second day), which is obviously difficult 

 to reconcile, or even quite out of harmony, with the 

 indisputable facts concerning the communication of 

 cholera by drinking water. It is also difficult to 

 believe in such rapid destruction of the cholera bacilli 

 taking place after their presence has now been on a 

 number of occasions demonstrated by the special 

 methods in question in various polluted natural waters^ 

 and we cannot help thinking that if these special 

 methods had been employed in such experiments as 

 those of Kraus, the cholera bacilli would have been 

 discovered after a much longer period of time. In this 

 connection we have always regarded as of great import- 

 ance some observations made by Gruber, in which such 

 special methods were used ('Wiener medicinische Wo- 

 chenschrift,' 1887, Nos. 7 and 8). In these experiments 

 he showed that when the cholera spirilla are mixed 

 with putrefactive bacteria, ' although the latter gain an 

 enormous numerical ascendency over the comma spirilla 



