PROGRESSIVE ELABORATION OF 'BLOOD. 295 



oil ; the latter bears a close resemblance to the serum of the blood, but 

 has some of the chyle-corpuscles suspended in it. Considerable diffe- 

 rences present themselves, however, both in the perfection of the coagu- 

 lation, and in its duration. Sometimes the chyle sets into a jelly-like 

 mass ; which, without any separation into coagulum and serum, liquefies 

 again at the end of half an hour, and remains in this state. The -coagu- 

 lation is usually most complete in the fluid drawn from the receptaculum 

 chyli and thoracic duct ; and here the resemblance between the floating 

 cells, and the white or colourless corpuscles .of the blood, becomes very 

 striking. 



520. The Lymph, or fluid of the Lymphatics, differs from the Chyle, 

 as already remarked, in its comparative transparency : its want of the 

 opacity or opalescence, which is characteristic of the latter, being due 

 to the absence, not merely of oil-globules, but also of the " molecular 

 base." It contains floating cells, which bear a close resemblance to 

 those of the Chyle on the one hand, and* to the colourless corpuscles of 

 the Blood on the other ; and these, as in the preceding case, are most 

 numerous in the fluid which is drawn from the lymphatics that have 

 passed through the glands, and in that obtained from the glands them- 

 selves. Lymph coagulates like chyle ; a colourless clot being formed, 

 which encloses the greater part of the corpuscles. The lacteals may be 

 regarded as the Lymphatics of the intestinal walls and mesentery; 

 performing the function of interstitial absorption, as well as effecting the 

 introduction of alimentary substances from without. During the inter- 

 vals of digestion, they contain a fluid, which is in all respects conform- 

 able to the lymph of the lymphatic trunks. 



521. Thus by the admixture of the aliment newly introduced from 

 without, with the matter which has been taken up in the various parts 

 of the system, and by the preparation which these undergo in their 

 course towards the thoracic duct, a fluid is prepared, which bears a 

 strong resemblance to blood in every particular, save the presence of 

 red corpuscles. Even these may sometimes be found in the contents 

 of the thoracic duct, in sufficient amount to communicate to them a 

 perceptible red tinge ; but it is doubtful whether they have not found 

 their way thither accidentally, some of the lymphatic or lacteal trunks, 

 which have been divided in the dissection necessary to expose the duct, 

 having taken up blood by their open mouths, and rapidly transmitted it 

 into the general receptacle. The fluid of the thoracic duct may be 

 compared to the blood of Invertebrated animals ; from which the red 

 corpuscles are almost or altogether absent ; but which contains white 

 or colourless corpuscles, and which possesses but a slight coagulating 

 power, in consequence of its small proportion of fibrine. And we 

 hence see, why these animals should require no special absorbent sys- 

 tem ; since the blood-vessels convey a fluid, which is itself so analogous 

 to the chyle and lymph to be absorbed, that the latter may be at once 

 introduced into it, without injuring its qualities. 



