IMMUNITY IN CHOLERA. 479 



passage of living vibrios into the small intes- 

 tines, and this is particularly true of cholera. 

 It is nevertheless evident that the barrier in many 

 instances is not a serious one. A number of cases 

 are recorded in which investigators while working 

 with cultures have become infected with cholera, 

 the cases running typical courses which sometimes 

 ended fatally (Pfeiffer, Pfuhl and others). Or- 

 ganisms which are ingested with water may pass 

 rapidly to the intestines without being affected by 

 the acid of the stomach, or when taken with food 

 they may be buried in the latter and hence not 

 come in contact with the gastric secretion. It 

 seems probable that the intestinal epithelium has 

 a certain resistance to invasion which is most mani- 

 fest in the case of those who do not become in- 

 fected in spite of the presence of the organisms in 

 their intestines. Natural immunity appears to be 

 one which is directed against the bacteria rather 

 than against the endotoxin, proliferation of the 

 organisms in the intestinal epithelium being pre- 

 vented. Poorly nourished individuals, the very 

 young and the very old are particularly suscepti- 

 ble. Other gastrointestinal disorders, in the pres- 

 ence of an epidemic, predispose to infection. De- 

 fects in the intestinal epithelium, or a decreased 

 resistance of the latter, may afford favorable 

 conditions for invasion. 



Active immunity, as that which results from in- Acquired 

 fection or from protective inoculation, is charac- Immiinlty ' 

 terized by the appearance of bactericidal ambocep- 

 tors, opsonins, agglutinins and specific precipitins 

 in the serum. 



Amako finds that opsonin, bactericidin and 

 agglutinin develop with the course of the disease. 



