SUSCEPTIBILITY AND IMMUNITY. 269 



(rothlauf bacillus). White mice are very susceptible to the patho- 

 genic action of this bacillus. But mice which, subsequently to in- 

 fection, were injected with the expressed and filtered tissue juices of 

 an immune rabbit, recovered, while the control animals succumbed. 

 According to Emmerich, the result in these experiments was due to 

 a destruction of the pathogenic bacilli in the bodies of the infected 

 animals ; and the statement is made that at the end of eight hours 

 after the injection of the expressed tissue juices all bacilli in the body 

 of the infected animal were dead. The same liquid did not, however, 

 kill the bacilli when added to cultures external to the body of an 

 animal. The inference, therefore, seems justified that the result de- 

 pends, not upon a substance present in the expressed juices of an 

 immune animal, but upon a substance formed in the body of the 

 animal into which these juices are injected. 



We have, however, an example of induced immunity in which 

 the result appears to depend directly upon the destruction of the 

 pathogenic microorganism in the body of the immune animal. In 

 guinea-pigs which have an acquired immunity against Vibrio Metsch- 

 nikovi the blood serum has been proved to possess decided germicidal 

 power for this "vibrio," whereas it multiplies readily in the blood 

 serum of non-immune guinea-pigs (Behring and Nissen). 



There is experimental evidence that animals may acquire an arti- 

 ficial immunity against the toxic action of certain toxalbumins from 

 other sources than bacterial cultures. Thus Sewell (1887) has shown 

 that a certain degree of tolerance to the action of rattlesnake venom 

 may be established by inoculating susceptible animals with small 

 doses of the " hemialbumose " to which it owes its toxic potency. 

 These results have been confirmed by the more recent experiments Of 

 Calmette (1894) and of Fraser (1895). In his paper detailing the 

 results of his experiments the first-named author says : 



' ' Animals may be immunized against the venom of serpents either by 

 means of repeated injections of doses at first feeble and progressively stronger, 

 or by means of successive injections of venom mixed with certain chemical 

 substances, among which I mention especially chloride of gold and the hypo- 

 chlorites of lime or of soda. 



"The serum of animals thus treated is at the same time preventive, anti- 

 toxic, and therapeutic, exactly as is that of animals immunized against 

 diphtheria or tetanus. 



"If we inoculate ascertain number of rabbits, under the skin of the 

 thigh, with the same dose, one milligramme of cobra venom for example, 

 and if we treat all of these animals with the exception of some for control, 

 by subcutaneous or intraperitoneal injections of the serum of rabbits im- 

 munized against four milligrammes of the same venom, all of the control 

 animals not treated will die within three or four hours, while all of the 

 animals will recover which receive five cubic centimetres of the therapeutic 

 serum within an hour after receiving the venom." 



In this connection we may remark that there is some evidence to 



