ABSORPTION. 411 



Some experiments on the absorption of various mineral and vegeta- 

 ble poisons have brought to light the singular fact that, in some cases, 

 absorption takes place more rapidly from the rectum than from the 

 stomach. Strychnia, for example, when in solution, produces its poi- 

 sonous effects much more speedily when introduced into the rectum 

 than into the stomach. When introduced in the solid form, however, 

 it is absorbed more rapidly from the stomach than from the rectum, 

 doubtless because of the greater solvent property of the secretion of the 

 former than of the latter. 



Conditions for Absorption. 1. The diffusibility of the substance to 

 be absorbed is one of the chief conditions for its absorption a col- 

 loid, as we have seen, dialyzes very little. It must be also in the liquid or 

 gaseous state. Mercury may, however, be absorbed even in the metallic 

 state; and in that state may pass into and remain in the blood-vessels, 

 or be deposited from them; and such substances as exceedingly finely- 

 divided charcoal, when taken into the alimentary canal, have been found 

 in the mesenteric veins. Oil, minutely divided, as in an emulsion, will 

 pass slowly into blood-vessels, as it will through a filter moistened with 

 water; but it is doubtful if fatty matters find their way into the blood- 

 vessels as they do into the lymph-vessels of ihe intestinal canal. 



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-ves- 

 sels 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 ab- 

 sorption of the poison not only by diminishing the velocity of the cir- 

 culation in the part, but by filling all its vessels too full to admit more. 



4. 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. 



These four conditions are physical, but (5) the vital condition of the 

 absorptive epithelium must not be forgotten. It has been shown, for 

 example, that the absorption by the frog's skin is hastened by alcohol 

 and retarded by chloroform. It appears also that absorption is retarded 

 rather than hastened by removal of the intestinal epithelium. 



