262 SUSCEPTIBILITY AND IMMUNITY. 



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 Msseii). 



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 a certain 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 

 show that persons who are repeatedly stung by certain poisonous in- 

 sects mosquitoes, bees acquire a greater or less degree of immu- 

 nit} r from the distressing local effects of their stings. 



Ehrlich, of Berlin, in 1891, reported his success in establishing 

 immunity in guinea-pigs against two toxalbumins of vegetable 

 origin: one ricin from the castor-oil bean (Ricinus communis), 

 the other abrin from the jequirity bean. The toxic potency 

 of ricin is somewhat greater than that of abrin, and it is esti- 

 mated by Ehrlich that one gramme of this substance would suffice 

 to kill one and a half millions of guinea-pigs. When injected be- 

 neath the skin, in dilute solution, it produces intense local inflamma- 

 tion, resulting in necrosis of the tissues. Mice are less susceptible 

 tfyan guinea-pigs and are more easily made immune. This is most 

 readily effected by giving them small and gradually increasing doses 

 with their food. As a result of this treatment the animal resists 



