424 CHOLERA. 



human subject, which are on the whole favourable, also supply 

 additional evidence. If all these facts are taken together, we 

 consider the conclusion must be arrived at that the growth of 

 Koch's spirillum in the intestine is the immediate cause of the 

 disease. This does not exclude the probability of an important 

 part being played by conditions of weather and locality, though 

 such are very imperfectly understood. Pettenkofer, for example, 

 recognised two main factors in the causation of epidemics, which 

 he designated x and y, and considered that these two must be 

 present together in order that cholera may spread. The x is the 

 direct cause of the disease an organism which he admitted 

 to be Koch's spirillum ; the y includes climatic and local con- 

 ditions, e.g., state of ground-water, etc. 



Difficulty does not arise, however, so much with regard to 

 the causal relationship of Koch's spirillum to cholera as in 

 connection with various organisms which have been culti- 

 vated from other sources, and which more or less closely 

 resemble it. 



Other Spirilla resembling the Cholera Organism. These 

 have been chiefly obtained either from water contaminated by 

 sewage or from the intestinal discharge in cases with choleraic 

 symptoms. Some of them differ so widely in their cultural and 

 other characters (some, for example, are phosphorescent) that no 

 one would hesitate to classify them as distinct species. Others, 

 however, closely resemble the cholera organism. 



The vibrio berolinensis, cultivated by Neisser from Berlin sewage water, 

 differs from the cholera organism only in the appearance of its colonies in 

 gelatin plates, its weak pathogenic action, and its giving a negative result with 

 Pfeiffer's test. It, however, gives the cholera-red reaction. The vibrio Danubi- 

 cus, cultivated by H eider from canal water, also differs in the appearance of its 

 colonies in plates, and also reacts negatively to Pfeiffer's test ; in most respects 

 it closely resembles the cholera organism. Another spirillum (v. Ivanoff) 

 was cultivated by Ivanoff from the stools of a typhoid patient after these had 

 been diluted with water. This organism differed somewhat in the appearance 

 of its colonies and in its great tendency to grow out in the form of long 

 threads, but Pfeiffer found that it reacted to his test in the same way as the 

 cholera organism, and he considered that it was really a variety of the cholera 

 organism. No spirilla could be found microscopically in the stools in this 

 case, and Pfeiffer is of the opinion that the organism gained entrance acci- 

 dentally. These examples will show how differences of opinion, even amongst 

 experts, might arise as to whether a certain spirillum were really the cholera 

 organism or a distinct species resembling it. 



