IMMUNITY. 173 



tigations have not fully confirmed this statement, they have led to 

 the discovery of many interesting facts. It has been found that at 

 least temporary immunity against some of the infections may be 

 secured by previous treatment of the animal with normal serum, 

 nucleinic acid, bouillon, or even physiological salt solution. For 

 instance, Issaeff,* found that animals can be protected against experi- 

 mental cholera peritonitis by previous intra-peritoneal injections of 

 the above-mentioned substances. This investigator found that im- 

 mediately after the preventive injection there is a marked diminution 

 in the number of leucocytes in the peritoneal lymph, but after a 

 short period of time the leucocytes return in increased numbers. 

 Now if at this stage the ordinarily fatal quantity of a culture of the 

 cholera vibrio be injected into the peritoneum, death does not follow. 

 In accordance with the phagocytic doctrine of Metschnikdff it is sup- 

 posed that these substances of non-bacterial origin give temporary 

 immunity on account of the phagocytosis which they induce. Tem- 

 porary immunity against some of the most highly virulent bacteria 

 may be secured in this manner. Thus Bordet succeeded in immuniz- 

 ing animals against most virulent cultures of the streptococcus by 

 previous treatment with ordinary nutritive bouillon. This form of 

 securing immunity is more easily demonstrated by peritoneal inocu- 

 lations than in any other way. It is possible that the injection of 

 the preventive substance leads to more or less phagolysis, and as a 

 result of this the peritoneal fluid becomes unusually rich in bacteri- 

 cidal substances, which result from the disintegration of the phago- 

 cytes. Metschnikoff further suggests that the phagolysis caused by 

 the introduction of the preventive solution is the active agent in 

 causing the accumulation of phagocytes at the place where the 

 phagolysis has occurred, which in this instance is in the peritoneal 

 cavity. On account of the phagolysis, due to the introduction of 

 such a substance as bouillon, the fluid content of the peritoneal cav- 

 ity becomes rich in dissolved bactericidal substances and in this re- 

 spect resembles certain blood sera. When the bacteria are subse- 

 quently injected into the peritoneal cavity many of them are destroyed 

 by the soluble germicidal substances, and those that escape this 

 action are seized upon by the incoming phagocytes. If a drop of 

 the peritoneal fluid be examined at this time it will be observed that 

 some of the bacteria have met with extra-cellular death, while oth- 

 ers are engulfed in the phagocytes. 



The most probable explanation of the good results obtained in 

 Pasteur's treatment of hydrophobia is that by this means a toxin 

 immunity is secured. The organism which is supposed to cause 

 hydrophobia has not as yet been discovered, but the probabilities 

 are that inoculation with a living organism is made by the bite of 

 the rabid dog. In this disease a long period of incubation precedes 

 ''■ Zdtschrift fiir Hygiene, 16, 1894. 



