3/0 ABSORPTION. 



hydrated alumina, hydrated silicic acid, etc. ; while the 

 crystalloids are characterised by qualities the reverse of 

 those just mentioned as belonging to colloids. Alcohol, 

 sugar, and ordinary saline substances are examples of 

 crystalloids. 



Absorption by blood-vessels is the consequence of their 

 walls being, like the membranous septum of the endos- 

 rnometer, porous and capable of imbibing fluids, and of 

 the blood being so composed that most fluids will mingle 

 with it. The process of absorption, in an instructive, 

 though very imperfect degree, may be observed in any 

 portion of vascular tissue removed from the body. If such 

 an one be placed in a vessel of water, it will shortly swell, 

 and become heavier and moister, through the quantity of 

 water imbibed or soaked into it ; and if now, the blood 

 contained in any of its vessels be let out, it will be found 

 diluted with water, which has been absorbed by the blood- 

 vessels and mingled with the blood. The water round the 

 piece of tissue also will become blood-stained ; and if all 

 be kept at perfect rest, the stain derived from the solution 

 of the colouring matter of the blood (together with which 

 chemistry would detect some of the albumen and other 

 parts of the liquor sanguinis) will spread more widely 

 every day. The same will happen if the piece of tissue be 

 placed in a saline solution instead of water, or in a solution 

 of colouring or odorous matter, either of which will give 

 their tinge or smell to the blood, and receive, in exchange, 

 the colour of the blood. 



Even so simple an experiment will illustrate the ab- 

 sorption by blood-vessels during life ; the process it shows 

 is imitated, but with these differences : that, during life, 

 as soon as water or any other substance is admitted into 

 the blood, it is carried from the place at which it was 

 absorbed into the general current of the circulation, and 

 that the colouring matter of the blood is not dissolved so 

 as to ooze out of the blood-vessels into the fluid which they 

 are absorbing. 



