TYPHOID FEVER. 381 Kolle, cannot be separated from the bodies of the bacilli producing it. Animals can easily be immunized to this bacillus, and then, according to Chanternesse and Widal, develop in their blood an antitoxic substance capable of protecting other animals. Sternl has also found that in the blood of human convalescents a substance exists which has a protective effect upon guinea-pigs. His observation is in accordance with a previous one by Chantemesse and Widal, and has recently been abundantly confirmed. The immunization of dogs and goats by the introduc- tion of increasing doses of virulent cultures has been achieved by Pfeiffer and Kolle2 and by Loffler and Abel.3 From these animals serums were secured not exactly an- titoxic, but anti-infectious or anti-microbic in operation, and possessed of marked specific germicidal action upon the typhoid bacilli when simultaneously introduced into the peritoneal cavity of guinea-pigs. The action of the typhoid serum is specific, and exerts exactly the same action upon the typhoid bacilli as the cholera serum exerts upon the cholera spirilla, killing and dissolving them (Pfeiffer's phenomenon). So far, no serum has been produced that is efficacious in human medicine. The specific reaction of the serum can be used to dif- ferentiate cultures of the colon and typhoid bacilli, the typhoid bacilli alone exhibiting the specific effect of the typhoid serum. Christophers4 found that the serum from typhoid patients occasionally caused agglutinations in cultures of the colon bacillus, but concludes that this does not lessen the specificity of the reaction, as there may be two combined specific actions of these serums. Experi- ments on rabbits established that typhoid and colon serums could be produced, each specific in its agglutin- 1 Zeitschrift fur Hygiene, xvi., 1894, p. 45$. 2 Ibid"> l896- 3 Centralbl.f. Bakt. u. Parasitenk., Bd. xix.,]STo. 23, p. 51, Jan. 23,1896. * Brit. Med. Jour., Jan. 8, 1898.