270 SUSCEPTIBILITY AND IMMUNITY. 



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

 sectsmosquitoes, bees acquire a greater or less degree of immu- 

 nity 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 

 than 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 

 subcutaneous injections of two hundred to four hundred times the 

 fatal dose for animals not having this artificial immunity. The fatal 

 dose of abrin is about double that of ricin. When injected into mice 

 in the proportion of one cubic centimetre to twenty grammes of body 

 weight a solution of one part in one hundred thousand of water 

 proved to be a fatal dose. The local effects are also less pronounced 

 when solutions of abrin are used ; they consist principally in an ex- 

 tensive induration of the tissues around the point of injection and a 

 subsequent falling off of the hair over this indurated area. When 

 introduced into the conjunctival sac, however, abrin produces a 

 local inflammation in smaller amounts than ricin, a solution of 1 : 800 

 being sufficient to cause a decided but temporary conjunctivitis. 

 Solutions of 1 : 50 or 1 : 100 of either of these toxalbumins, introduced 

 into the eye of a mouse, give rise to a panophthalmitis which com- 

 monly results in destruction of the eye. But in mice which have 

 been rendered immune by feeding them for several weeks with food 

 containing one of these toxalbumins, no reaction follows the intro- 

 duction into the eye of the strongest possible solution, or of a paste 

 made by adding abrin to a little ten-per-cent salt solution. Ehrlich 

 gives the following explanation of the remarkable degree of im- 

 munity established in his experiments by the method mentioned: 



" All of these phenomena depend, as may be easily shown, upon 

 the fact that the blood contains a body antiabrin which completely 

 neutralizes the action of the abrin, probably by destroying this body." 



In a more recent paper Ehrlich has given an account of subse- 

 quent experiments which show that the young of mice which have 

 an acquired immunity for these vegetable toxalbumins may acquire 

 immunity from the ingestion of the mother's milk ; and also that 

 immunity against tetanus may be acquired in a very brief time by 



