372 ABSORPTION. 



Carbonate of lithia, when taken in five or ten grain doses 

 on an empty stomach, may be detected in the urine in 5 or 

 I O minutes ; or, if the stomach be full at the time of taking 

 the dose, in 20 minutes. It may sometimes be detected in 

 the urine, moreover, for six, seven, or even eight days. 



Some experiments on the absorption of various mineral 

 and vegetable poisons, by Mr. Savory, 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 

 poisonous 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 that of the latter. 



With regard to the degree of absorption by living blood- 

 vessels, much depends on the facility with which the sub- 

 stance to be absorbed can penetrate the membrane or tissue 

 which lies between it and the blood-vessels ; for, naturally, 

 the blood-vessels are not bare to absorb. Thus absorption 

 will hardly take place through the epidermis, but is quick 

 when the epidermis is removed, and the same vessels are 

 covered with only the surface of the cutis, or with granula- 

 tions. In general, the absorption through membranes is in 

 an inverse proportion to the thickness of their epithelia ; 

 so Miiller found the urinary bladder of a frog traversed in 

 less than a second ; and the absorption of poisons by the 

 stomach or lungs appears sometimes accomplished in an 

 immeasurably small time. 



The substance to be absorbed must, as a general rule, be 

 in 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 blood-vessels, or be 



