3IO MICRO-ORGANISMS AND DISEASE [chap. 



that the diphtheria bacillus does not cause this peritonitis 

 even if injected into the peritoneal cavity in a living state. If 

 from an active gelatine culture (slanting surface) the growth 

 is scraped off and distributed in sterile bouillon, and of this 

 suspension one-sixth is injected subcutaneously into a 

 guinea-pig of 500-700 grammes weight, the typical tumour 

 is produced, and death occurs in thirty or thirty-six 

 hours with certainty, but the same dose of the same 

 culture injected into the peritoneal cavity of a guinea-pig 

 half that weight does not cause fatal illness. If from the 

 peritoneal fluid a little is withdrawn two, three, four, and 

 six hours after the intraperitoneal injection of the large dose 

 of living diphtheria baciUi, and examined, it "will be found 

 that most of the bacilli are dead already after two hours, and 

 that no living bacilli (no successful subculture) can be estab- 

 lished after four to six hours. Such guinea-pigs as had been 

 once intraperitoneally injected with more than about a 

 double, otherwise fatal, dose of living gelatine culture can 

 repeatedly at intervals be injected with increasing amounts 

 ^at the fifth injection as much as one-third of a living 

 gelatine culture can be introduced intraperitoneally — that 

 is to say, an otherwise fourfold fatal dose— without producing 

 any illness. Moreover, such guinea-pigs appear also immu- 

 nised against an otherwise fatal dose of living diphtheria 

 baciUi subcutaneously injected, no tumour and no disease is 

 hereby produced. By these and other similar experiments to 

 be mentioned in the chapter on Immunity, I have been able 

 to show that the specific immunising or germicidal power 

 against a bacterial species which the blood-serum of repeatedly 

 intraperitoneally injected (immunised) guinea-pigs acquires 

 (R. Pfeiffer) is related to substances derived from the bacilli 

 themselves that had been introduced into the peritoneum, 

 and had been used for the immunisation. 



