ABSORPTION BY BLOOD-VESSELS. 373 



deposited from them (Oesterlen) ; and such substances as 

 exceedingly finely-divided charcoal, when taken into the 

 alimentary canal, have been found in the mesenteric veins 

 (Oesterlen) ; the insoluble materials of ointments may also 

 be rubbed into the blood-vessels ; but there are no facts to 

 determine how these various substances effect their pass- 

 age. Oil, minutely divided, as in an emulsion, will pass 

 slowly into blood-vessels, as it will through a filter mois- 

 tened with water (Vogel); and, without doubt, fatty matters 

 find their way into the blood-vessels as well as the lymph- 

 vessels of the intestinal canal, although the latter seem to 

 be specially intended for their absorption. 



As in the experiments before referred to, the less dense 

 the fluid to be absorbed, the more speedy, as a general 

 rule, is its absorption by the living blood-vessels. Hence 

 the rapid absorption of water from f the stomach; also of 

 weak saline solutions ; but with strong solutions, there 

 appears less absorption into, than effusion from, the blood- 

 vessels. 



The absorption is the less rapid the fuller and tenser the 

 blood-vessels are ; and the tension may be so great as 

 to hinder altogether the entrance of more fluid. Thus, 

 Magendie found that when he injected water into a dog's 

 veins to repletion, poison was absorbed very slowly; but 

 when he diminished the tension of the vessels by bleeding, 

 the poison acted quickly. So, when cupping-glasses are 

 placed over a poisoned wound, they retard the absorption 

 of the poison, not only by diminishing the velocity of the 

 circulation in the part, but by filling all its vessels too full 

 to admit more. 



On the same ground, absorption is the quicker the more 

 rapid the circulation of the blood ; not because the fluid 

 to be absorbed is more quickly imbibed into the tissues, or 

 mingled with the blood, but because as fast as it enters 

 the blood, it is carried away from the part, and the blood, 

 being constantly renewed, is constantly as fit as at the first 

 for the reception of the substance to be absorbed. 



