IMBIBITION AND EXHALATION. 307 



CHAPTER XV. 



IMBIBITION AND EX HAL ATI ON. THE LYMPHATIC 



SYSTEM. 



DURING the passage of the blood through the capillaries of the 

 circulatory system, a very important series of changes takes place 

 by which its ingredients are partly transferred to the tissues by 

 exhalation, and at the same time replaced by others which the blood 

 derives by absorption from the adjacent parts. These phenomena 

 depend upon the property, belonging to animal membranes, of 

 imbibing or absorbing certain fluid substances in a peculiar way. 

 They are known more particularly as the phenomena of endosmosis 

 and exosmosis. 



These phenomena may be demonstrated in the following way. If 

 we take two different liquids, for example a solution of salt and an 

 equal quantity of distilled water, and inclose them in a glass vessel 

 with a fresh animal membrane stretched between, so that there is 

 no direct communication from one to the other, the two liquids 

 being in contact with opposite sides of the membrane, it will be 

 found after a time that the liquids have become mixed, to a cer- 

 tain extent, with each other. A part of the salt will have passed 

 into the distilled water, giving it a saline taste ; and & part of the 

 water will have passed into the saline solution, making it more 

 dilute than before. If the quantities of the two liquids, which 

 have become so transferred, be measured, it will be found that a 

 comparatively large quantity of the water has passed into the 

 saline solution, and a comparatively small quantity of the saline 

 solution has passed out into the water. That is, the water passes 

 inward to the salt more rapidly than the salt passes outward to the 

 water. The consequence is, that an accumulation soon begins to 

 show itself on the side of the salt. The saline solution is increased 

 in volume and diluted, while the water is diminished in volume, 

 and acquires a saline ingredient. This abundant passage of the 

 water, through the membrane, to the salt, is called endosmosis ; and 



