HO EXPERIMENTAL EVOLUTION LECT. 



destroyed by their passage through the liver for 

 instance. 



Secondly, the age of tJie animal under experiment. 

 This is easily ascertained, and the fact is recognised 

 in medical practice, where the dose of the same drug 

 varies from one-sixteenth to one, according as it is 

 given to a young child or to an adult. 



Thirdly, sex. Females are more sensitive than 

 males, and accordingly are unable to withstand doses 

 of drugs or poisons which males resist. 



Fourthly, species. Belladonna is very active on 

 man, cat, dog, and birds ; less so on horses and hogs ; 

 nearly without effect upon sheep and goats, and 

 especially on rabbits. Within the same class the 

 same differences obtain ; the rat is, generally 

 speaking, more sensitive than the guinea-pig, 

 and the rabbit is less so than the latter ; and the 

 ass is more sensitive than the mule and the horse. 

 Hemlock (Conium macnlatuni} is not injurious for the 

 lark and quail ; although they may eat so much of it 

 that their flesh may be poisonous for Carnivora, they 

 themselves sustain no injury. The red corn poppy is 

 not injurious for rabbits, and it is said that Euphorbia 

 may be eaten without inconvenience by goats, although 

 it confers toxic properties on their milk. Laburnum 

 is not toxic for goats, rabbits, and hares. Within the 

 same species, marked differences obtain between 



