ABSORPTION. 305 



cervical pair are not always synchronous with those of the pair in the 

 ischiatic region, and even the corresponding sacs of opposite sides are not 

 always synchronous in their action. 



Unlike the contractions of the blood-heart, those of the lymph-heart 

 appear to be directly dependent upon a certain limited portion of the 

 spinal cord. For Volkmann found that so long as the portion of spinal 

 cord corresponding to the third vertebra of the frog was uninjured, the 

 cervical pair of lymphatic hearts continued pulsating after all the rest of 

 the spinal cord and the brain were destroyed; while destruction of this 

 portion, even though all other parts of the nervous centres were unin- 

 jured, instantly arrested the heart's movements. The posterior, or ischi- 

 atic, pair of lymph-hearts were found to be governed, in like manner, by 

 the portion of spinal cord corresponding to the eighth vertebra. Division 

 of the posterior spinal roots did not arrest the movements; but division 

 of the anterior roots caused them to cease at once. 



Absorption by Blood-vessels. In the absorption by the lym- 

 phatic or lacteal vessels just described, there appears something like the 

 exercise of choice in the materials admitted into them. But the absorp- 

 tion by blood-vessels presents no such appearance of selection of materials; 

 rather, it appears, that every substance, whether gaseous, liquid, or a 

 soluble, or minutely divided solid, may be absorbed by the 

 blood-vessels, provided it is capable of permeating their 

 walls, and of mixing with the blood; and that of all such 

 substances, the mode and measure of absorption are deter- 

 mined solely by their physical or chemical properties and 

 conditions, and by those of the blood and the walls of the 

 blood-vessels. 



Osmosis. The phenomena are, indeed, to a great ex- 

 tent, comparable to that passage of fluids through mem- 

 brane, which occurs quite independently of vital conditions, 

 and the earliest and best scientific investigation of which 

 was made by Dutrochet. The instrument which he employed 

 in his experiments was named an endosmometer. It may con- 

 sist of a graduated tube expanded into an open-mouthed bell 

 at one end, over which a portion of membrane is tied (Fig. 

 218). If now the bell be filled with a solution of a salt 

 say sodium chloride, and be immersed in water, the water 

 will pass into the solution, and part of the sali will pass out FIG. 218. En- 



. , ... dosmometer. 



into the water; the water, however, will pass into the solu- 

 tion much more rapidly than the salt will pass out into the water, and the 

 diluted solution will rise in the tube. To this passage of fluids through 

 membrane the term Osmosis is applied. 



The nature of the membrane used as a septum, and its affinity for the 

 fluids subjected to experiment, have an important influence, as might be 

 anticipated, on the rapidity and duration of the osmotic current. Thus, 

 VOL. I. 20. 



