312 HANDBOOK OF PHYSIOLOGY. 



of imbibing fluids, and of the blood being so composed that most fluids 

 will mingle with it. Thus the relation of the chyme in the stomach 

 and intestines to the blood circulating in the vessels of the gastric and 

 i intestinal mucous membrane is evidently just that which is required for 

 : osmosis. The chyme contains substances which have been so acted 

 upon by the digestive juices as to have become quite able to pass through 

 an animal membrane, or to dialyze as it is called. The thin animal mem- 

 brane is the coat of the blood-vessels with the intervening mucous mem- 

 brane. The nature of the fluid within the vessels, the very feeble power 

 of dialyzation which the albuminous blood possesses, determines the di- 

 rection of the osmotic current, viz., into and not out of the blood-ves- 

 sels. The current is of course aided by the fact of the constant change 

 in the blood presented to the osmotic surface, as it rapidly circulates 

 within the vessels. As a rule the current is from the stomach or intes- 

 tine into the blood, but the reversed action may occur, when, for ex- 

 ample, a certain salt, e. g., sulphate of magnesia, is taken into the 

 stomach, in which case there is a rapid discharge of water from the 

 blood-vessels into the alimentary canal resulting in purgation. The 

 presence of various substances in the food has the power of diminishing 

 the rate of absorption, their influence is probably exerted upon the mem- 

 brane, diminishing its power of permitting osmosis. Whereas the pres- 

 ence of a little hydrochloric acid in the contents of the stomach appears 

 to determine the direction of the osmosis, or at any rate to diminish or 

 prevent exosmosis. 



The conditions for osmosis exist not only in the alimentary mucous 

 membrane, but also in the serous cavities and the tissues elsewhere. 



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 a 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 coloring 

 matter of the blood, together with 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 coloring or odorous matter, either of which 

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

 color of the blood. 



Various substances have been classified according to the degree in 

 which they possess the property of passing, when in a state of solution 

 in water, through membrane; those which pass freely, inasmuch as they 

 are usually capable of crystallization, being termed crystalloids, and 



