54 MECHANISM OF ABSORPTION. 



That no substance can exert any influence on the 

 whole system unless the circulation of the blood, 

 through the vessels of the part to which it may be 

 applied, is performed with a certain degree of activity. 



That the circulation of the blood must precede 

 and accompany the act of general absorption is, 

 among many other instances, proved by the follow- 

 ing experiments : 



1. Magendie divided all the parts of the thigh of 

 an animal but the femoral vessels, and then inserted 

 poison under the integuments of the limb. While 

 the vein was compressed no symptoms appeared, but 

 they were immediately produced when the return of 

 the blood was unimpeded. 



2. Emmert tied the abdominal aorta, and intro- 

 duced poison into a wound in the foot, but at the 

 end of seventy hours no effects had appeared. The 

 vessel being then liberated the poison (prussic acid) 

 acted within half an hour. I have repeated the 

 experiment with precisely similar results. The aorta 

 being compressed, a few drops of a strong solution 

 of hydrosulphate of ammonia were introduced 

 beneath the integuments of the thigh. At the end 

 of seven minutes no symptoms of poisoning had 

 appeared, but on then releasing the vessel the opera- 

 tion of the poison was immediately evident, and the 

 animal was dead in less than a minute. A number 

 of similar facts might be adduced in support of this 

 point, but it will be sufficient to refer for them to 

 any modern work on physiology. 



This principle being established, we may, in the 

 next place, proceed to inquire how the action of the 



