ACQUIRED IMMUNITY 81 



made immune against the action of certain toxic pro- 

 teids of vegetable origin, other than those produced 

 by bacteria, one, ricin, from the castor-oil bean, the 

 other, abrin, from the jequirity bean. The toxic po- 

 tency of ricin is somewhat greater than that of abrin, 

 but both are far more poisonous than strychnin. A 

 small quantity of a solution containing one part in 

 one hundred thousand parts of water will quickly kill 

 a mouse. But when injected into these animals in 

 still smaller and non-fatal doses, or given to them 

 with their food, immunity may be established to such 

 a degree that they resist subcutaneous injections of 

 two hundred to four hundred times the quantity re- 

 quired to kill a non-immune animal. 



In a later paper (1892), Ehrlich has given an account 

 of subsequent experiments which show that the young 

 of mice, which have an acquired immunity for these 

 vegetable poisons, acquire immunity from the inges- 

 tion of their mother's milk ; and also that immunity 

 from tetanus may be acquired in a brief time by 

 young mice through their mother's milk. 



These results have been confirmed by other observ- 

 ers and show that some substance upon which ac- 

 quired immunity depends is present in the milk of an 

 immune animal. 



