298 ABSOKPTION. 



the liquid or gaseous state, or, if a solid, must be soluble in the 

 fluids with which it is brought in contact. Hence the marks 

 of tattooing, and the discoloration produced by nitrate of silver 

 taken internally, remain. Mercury may be absorbed even in 

 the metallic state ; and in that state may pass into and remain 

 in the bloodvessels, or be deposited from them (Oesterlen) ; 

 and such substances as exceedingly finely-divided charcoal, 

 when taken into the alimentary canal, have been found in the 

 raesenteric veins (Oesterlen) ; the insoluble materials of oint- 

 ments may also be rubbed into the bloodvessels ; but there are 

 no facts to determine how these various substances effect their 

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

 slowly into bloodvessels, as it will through a filter moistened 

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

 their way into the bloodvessels as well as the lymphvessels 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 bloodvessels. Hence the rapid ab- 

 sorption of water from the stomach ; also of weak saline solu- 

 tions ; but with strong solutions, there appears less absorption 

 into, than effusion from, the bloodvessels. 



The absorption is the less rapid the fuller and tenser the 

 bloodvessels 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 diminish- 

 ing 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. 



