Comparative Physiology. 577 



and attraction and rejDulsion, in the descent and course of the 

 elaborated sap down the bark and along the medvillary rays, 

 and perhaps also in masses of smaller vessels, to furnish the 

 nutriment needed for the different parts of the system, the 

 power of endosmose is an assistant in the circulation, in such as 

 the bursting of anthers, capsules, &c., and generally wherever 

 thinner fluids are attracted to the more dense. If it is correct, 

 as stated, that endosmose often takes place from thicker to 

 thinner fluids, it may be found more general than supposed 

 through the circulation. If due to electricity, it may also be 

 found that the same electricity which produces the elective 

 affinity of the physical causes, may likewise be concerned, by 

 acting on the excitability of the membrane, in causing the much 

 greater power of endosmose through organised membrane, than 

 through porous inorganic septa, which is found to take place. 



In Chap. VII., On Interstitial Absorption, he says : — " The 

 circulating system not only serves to convey to the remoter 

 parts of the organism the materials required for the nutrition of 

 their tissues, but in the lower animals returns to the central 

 reservoir the portion which has not been so employed, and those 

 particles of the solid structure which, from tendency to decom- 

 pose or other causes, are unfit to be retained in it. In the 

 Vertebrata, which possess a special set of vessels for the ab- 

 sorj^tion of chyle from the intestines, allowing the portion not 

 absorbed to pass on and be rejected, we find also a system of 

 tubes ramifying through every part, to which the function of 

 absorption seems more particularly delegated. The lymphatics, 

 as they are termed, are distributed through almost every tissue 

 in the body ; they are especially abundant beneath the skin, 

 forming a close network so universally diffused, that, if success- 

 fully injected, it is scarcely possible to find a spot not traversed 

 by them. They commence, like the lacteals, without open ex- 

 tremities, deriving their contents by imbibition or endosmose 

 from the surrounding tissue ; they unite into large trunks, and 

 by these the fluid taken up by the absorbent extremities is 

 conveyed to the principal veins. The cause of motion in the 

 lymphatics, besides the endosmose one of absorption, is pi'obably 

 peristaltic, by which their fluids are propelled forward, the reflux 

 being prevented by the valves with which they are plentifully 

 supplied. The veins themselves, in many cases, participate in 

 the function of absorption more actively than the lymphatics." 

 The lymj^li taken up in this way is said to be nearly identical 

 witli the fluid portion of the blood, or serum, containing the 

 portion called serosity, supposed to consist partly of effete 

 particles, furnishing the matter excreted by the kidneys, &c. 

 The waste of the system is supposed to be taken up by these 

 means and conveyed into the circulation, where part of the car- 



