180 CLINICAL BACTERIOLOGY. 



method of immunization consists in the employment of the 

 ordinary unheated and unfiltered bouillon-culture. Many 

 experimental animals possess a considerable degree of 

 immunity to the typhoid-bacillus, and there is no great dif- 

 ficulty in increasing this. The animal is treated once or 

 twice with an intraperitoneal injection of half that amount 

 of bouillon-culture that is just necessary to cause death. 

 After from three to five days the animal will be able to 

 withstand this previously lethal amount, and after several 

 days, one and a half times, then twice, thrice, etc., this 

 dose can be injected. In this way a high degree of immu- 

 nity can rapidly be induced. The blood-serum of the 

 immunized animals is in turn capable of conferring immu- 

 nity upon untreated animals. 



As R. PfeifTer and his pupils assume, the blood-serum of 

 typhoid convalescents and of animals immune to typhoid 

 fever does not contain antitoxic, but only lysogenic pro- 

 tective substances (p. 62) that is, the serum, injected into 

 the peritoneal cavity of guinea-pigs simultaneously with 

 living typhoid-bacilli, causes dissolution of the specific 

 microorganisms. If two milligrams of a fresh, virulent 

 agar-culture that has been sterilized by exposure for several 

 hours in the thermostat at a temperature of 56 C. (132.8 

 F.) are injected into human beings, after a brief period of 

 indisposition the blood-serum of such persons likewise 

 possesses lysogenic properties. The strength of the lyso- 

 genicity attains the same degree as is present in the typhoid 

 convalescent, and the standard of the serum equals about 

 o.oi (p. 63). If the appearance of the specific bactericidal 

 (lysogenic) substances in the blood of individuals that have 

 suffered from typhoid fever is really, as Pfeiffer assumes, the 

 essential cause of immunity, then, according to the experi- 

 ments just described, it must also be possible, by means of 

 prophylactic injections of minimal amounts of the dead 

 bodies of typhoid-bacilli, to induce immunity of like degree 

 and duration. The decision of this most important ques- 

 tion must await the results of further investigation. 



Attempts at cure with protective serum or with milk ob- 

 tained from an immunized animal have been made only on a 

 small scale, and distinct success has not as yet been observed. 

 This is in harmony with the view already expressed that 



are designated plasmins, and the expressed juice of typhoid-bacilli correspond- 

 ingly as typhoplasmin.) 



