THE SPIRILLA 153 



10 c.c. of a 5 per cent, solution of a highly agglutinating 

 serum. After standing for two or three hours at room- 

 temperature, the mixture is centrifuged and the clear 

 supernatant fluid decanted. (6) The agglutinating power 

 of the latter on the organism with which the serum was 

 prepared is ascertained. If the organism treated in (a) is 

 homologous with the organism with which the agglutin- 

 ating serum was prepared, the decanted fluid will have lost 

 most, or a considerable proportion, of its agglutinating 

 power for the latter (Hewlett). 



Fixation Test. (See p. 20). 



Pfeiffer's reaction (p. 22) is particularly valuable in the 

 diagnosis of cholera. 



Pathogenesis. In Asiatic cholera urine is suppressed, 

 and the copious and watery stools have the characteristic 

 rice-water appearance due to flakes of detached epithelium. 

 The most prominent symptoms are subnormal tempera- 

 ture, distension of the abdomen, and ultimately profound 

 collapse. 



The organisms are practically confined to the intestine, 

 and are not to be found in other organs nor in the 

 blood. Death may occur in twelve or even six hours 

 after infection, or three hours after the first symptoms 

 are noticed. The incubation period rarely exceeds two or 

 three days. 



Unless some heroic measure, such as a device to 

 neutralise the acidity of the gastric juice, be employed, 

 experiments on animals fail to produce cholera. Intra- 

 peritoneal injections into guinea-pigs, though fatal, do 

 not produce cholera. Young suckling rabbits are an 

 exception, ingestion of the organism producing choleraic 

 diarrhoea. 



Occurrence and Distribution. The disease is endemic 

 in many parts of India, particularly the delta of the 

 Ganges. In other countries its course may be traced 

 along the ordinary lines of traffic, showing that it is 

 carried by travellers. There has been no epidemic of 

 cholera in the British Isles during recent years. 



Cholera spreads most rapidly when the earth tempera- 

 ture is high; this happens chiefly when the ground-water 

 is low, which is in accord with the observation of Petten- 

 kofer that increase in cholera is often preceded by a fall 

 in the ground -water. 



