396 CHOLERA. 



from cholera is another point in its favour, though further 

 evidence under this head is desirable. Fifthly, bacterio- 

 logical methods, which proceed on the assumption that 

 Koch's spirillum is the cause of the disease, have been of the 

 greatest value in the diagnosis of the disease. And lastly, 

 the results of Haffkine's method of preventive inoculation 

 in the 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 con- 

 ditions of weather and locality, though such are very 

 imperfectly understood. Pettenkofer, for example, recog- 

 nises two main factors in the causation of epidemics, which 

 he designates x and y, and considers 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 now admits to be Koch's spirillum ; the y includes 

 climatic and local conditions, 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 

 cultivated 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 con- 

 taminated 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 gelatine plates, its weak pathogenic action, and its giving a 

 negative result with Pfeiffer's test. It, however, gives the cholera-red 

 reaction. The vibrio Danubicus, cultivated by Heider from canal 

 water, also differs in the appearance of its colonies in plates, and also 



