Immunity 457 



from the dejecta of healthy individuals and those suffering 

 from other diseases. There is no satisfactory proof of the 

 specific nature of the organisms to be obtained by experi- 

 mentation upon animals. Animals are never affected by 

 any disease similar to cholera during epidemics, nor do foods 

 mixed with cholera discharges or with pure cultures of the 

 cholera spirillum affect them. Subcutaneous inoculations 

 do not produce cholera. 



Detection of the Organism. It often becomes a matter 

 of importance to detect the cholera spirilla in drinking- 

 water, and, as the number in which the bacteria exist in 

 such a liquid may be very small, difficulty may be experienced 

 in finding them by ordinary methods. One of the most 

 expeditious methods is that recommended by LofHer, who 

 adds 200 c.c. of the water to be examined to 10 c.c. of 

 bouillon, allows the mixture to stand in an incubator for 

 from twelve to twenty-four hours, and then makes plate 

 cultures from the superficial layer of the liquid, where, if 

 present, the development of the spirilla will be most rapid 

 because of the free access of air. A similar method, sug- 

 gested by Schottelius (see page 451), can be used to detect 

 the spirilla in feces. 



Immunity. Gruber and Wiener, * Haffkine, f Pawlow- 

 sky, J and Pfeiffer have immunized animals against toxic 

 substances from cholera cultures or against living cultures. 

 There seems, according to the researches of Pfeiffer, to 

 be no doubt that a protective substance exists in the blood 

 of immunized animals. In the peritoneal infection of 

 guinea-pigs the spirilla grow vigorously in the peritoneal 

 cavity, and can be found in immense numbers after from 

 twelve to twenty-four hours. If, however, together with 

 the culture used for inoculation, a few drops of the serum 

 from an immunized animal be introduced, Pfeiffer found 

 that, instead of multiplying, the organisms underwent a 

 peculiar granular degeneration and disappeared, the unpro- 

 tected animal dying, the protected animal remaining well. 

 This bacteriolytic change takes place as well in the test- 

 tube as in the peritoneal cavity. 



* "Centralbl. f. Bakt.," etc., 1892, xiv, p. 76. 



t "Le Bull, med.," 1892, p. 1113, and "Brit. Med. Jour.," 1893, 

 p. 278. 



J " Deutsche med. Wochenschrift," 1893, No. 22. 

 " Zeitschrift fur Hygiene," Bd. xvni and xx. 



