INFECTION. 133 



young. On the other hand, animals vaccinated with 

 cowpox have not been found to have immune offspring. 

 Toxins injected into the parents apparently do not pass 

 the placenta; but antitoxins do, giving thus a slight 

 transitory passive immunity. A slight immunity is 

 also given by immune mothers through their milk, a 

 small amount of antitoxic substance being absorbed. 



