ANATOMY AND PHYSIOLOGY 11 



and nutrition, as tonics of various kinds, require time for 

 the accomplishment of their mission, and are usually given 

 two or three times daily for a period of some weeks. 



Anatomy and Physiology. 



Certain differences in the action of medicines may be 

 observed as occuring in the various species of animals, and 

 in animals as contrasted in this respect with man. 



ACTION OF DRUGS ON ANIMALS AS COMPARED WITH THAT ^ MAN. 



From a comparative standpoint the action of drugs on 

 the nervous system of animals differs from that on man. 

 This follows according to the "law of dissolution," which 

 teaches that the more highly developed a part of the ner- 

 vous system is in the evolutionary scale, the more sensitive 

 is it to the influence of drugs. Since the cerebrum of man 

 is relatively larger and more highly developed, in propor- 

 tion to his weight, than is the case in animals, and since the 

 spinal cord is larger and more highly developed in pro- 

 portion to the brain in animals, it happens that drugs 

 impressing the nervous system exert less effect on the brain, 

 and more on the spinal cord, of animals than they do in man. 



Thus opium is more powerful in its influence on the 

 brain of man, and strychnin is more potent in its action on 

 the spinal cord of animals. Drugs are not absorbed so 

 rapidly or perfectly in the enormous digestive apparatus of 

 ruminants as in man; neither do emetics act in these animals, 

 nor in horses; while in none of the lower animals are agents 

 causing sweating so efficient as in man. 



ACTION OF DRUGS ON HORSES AS COMPARED WITH THAT ON OTHER 



ANIMALS. 



Differences exist relative to the action of drugs on the 

 horse, as compared with other animals, chiefly in respect 

 to the digestive apparatus. Emetics do not act on the horse, 

 as this animal does not vomit unless the stomach is greatly 

 distended with gas, which causes dilatation of the cardiac 



