308 HAND-BOOK OF PHYSIOLOGY. 



2. The less dense the fluid to be absorbed, the more speedy, as a gen- 

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

 absorption of water from the stomach; also of weak saline solutions; but 

 with strong solutions, there appears less absorption into, than effusion 

 from, the blood-vessels. 



3. 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, if water is injected into a dog's veins to repletion, 

 poison is absorbed very slowly; but when the tension of the vessels is 

 diminished by bleeding, the poison acts 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 cir- 

 culation 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. 



