188 PUBLIC HEALTH BACTERIOLOGY 



bacteria. " Tuberculo-plasmin " after filtration is a clear 

 pale yellow fluid, containing nucleo-albumin, which keeps 

 indefinitely on addition of 20 per cent of glycerin and 

 5 per cent of NaCl. This preparation has been used with 

 favourable results in guinea-pig tuberculosis. 



The reaction which follows the injection of a dead 

 culture (local pain and swelling, rigor, depression, and 

 anorexia) is not peculiar to any one bacterium, but 

 follows upon the subcutaneous injection of all bacterial 

 emulsions, and even of innocuous and living bacteria 

 (Buchner, 1890). 



4. With Soluble Toxins or Filtrates. This method was 

 first successfully used by Salmon and Smith, who showed 

 that pigeons could be rendered immune to hog cholera 

 by treatment \vith filtrates of hog-cholera bacilli (1886). 

 It is now used for the immunization of horses to diphtheria 

 and tetanus toxins, the immunity being afterwards 

 heightened by the injection of virulent cultures, if Behring's 

 advice is adopted. This use followed on the observations 

 of Roux and Yersin, who showed in 1886, as a " result 

 of splendid research " (Buchner) that the poison of 

 diphtheria is extremely susceptible to heat (being destroyed 

 at 65 C.), and is carried down mechanically by chemical 

 precipitates such as calcium phosphates, properties which 

 until then had been recognized mainly in the digestive 

 ferments or enzymes. Brieger and Fraenkel confirmed 

 these results, and showed that the poisons or toxins of 

 diphtheria and tetanus can be obtained in a moderately 

 pure form by precipitation \\ith absolute alcohol. These 

 poisons gave the reactions of albuminous substances, 

 and were hence at first called " toxalbumins." As they 

 are now believed to be non-proteid, the name " specific 

 toxins " is to be preferred. A specific toxin is one which, 

 on injection, causes all the symptoms of the infection in 

 question. 



5. Active Immunization by Feeding has been successfully 

 used by Ehrlich for the poisons ricin and abrin, and with 

 less success by Fraser against snake venom. In bacterial 

 infections it has proved, so far, tedious, and the immuni- 

 zation slight in amount. 



(c). By Passive Immunization. Behring in 1890 



