334 ABSORPTION. 



acetic acid, but are dissolved by ammonia. They are regarded by Robin as a variety of 

 leucocytes and are described by him as free nuclei. They make their appearance in the 

 blastema before the larger leucocytes are developed. 



Origin and Function of the Lymph. There can hardly be any doubt concerning the 

 source of most of the liquid portions of the lymph, for they can be derived only from the 

 blood. Although the exact relations between the smallest lymphatics and the blood- 

 vessels have not been made out in all parts of the system, there is manifestly no ana- 

 tomical reason why the water, mixed with albuminoid matters and holding salts in solu- 

 tion, should not pass from the blood into the lymphatics ; and this is rendered nearly 

 certain if it can be demonstrated that the lymphatics partly or entirely surround many 

 of the blood-vessels, for, under these circumstances, endosmotic and exosmotic currents 

 would inevitably take place. We have seen, in comparing the composition of the lymph 

 with that of the plasma of the blood, that the constituents of these fluids are nearly if 

 not quite identical ; the only variations being in their relative proportions. This is an- 

 other strong argument in favor of the passage of most of the constituents of the blood 

 into the lymph. 



One of the most important physiological facts in the chemical history of the lymph is 

 the constant existence of a considerable proportion of urea. This cannot be derived from 

 the blood, for its proportion is greater in the lymph, notwithstanding that this fluid is 

 being constantly discharged into the blood-vessels. The urea which exists in the lymph 

 is derived from the tissues ; it is discharged then into the blood, and is constantly being 

 removed from this fluid by the kidneys. 



The positive facts upon which to base any precise ideas with regard to the general 

 function of the lymph are not very numerous. From the composition of this fluid, its 

 mode of circulation, and the fact that it is being constantly discharged into the blood, it 

 would not seem to have an important function in the active processes of nutrition. The 

 experiments of Collard de Martigny sustain this view, inasmuch as the quantity and the 

 proportion of solid constituents of the lymph were rather increased than diminished in 

 animals that had been deprived of food and drink for several days; while it is well known 

 that starvation always impoverishes the blood from the first. On the other hand, urea, 

 one of the most important of the products of destructive metamorphosis of the tissues, is 

 undoubtedly taken up by the lymph and conveyed in this fluid to the blood. It re- 

 mains now for future investigations to determine whether other excrementitious princi- 

 ples may not be taken up from the tissues in the same way a question of great importance 

 in its relations to the mechanism of excretion. 



What is positively known with regard to the functions of the lymph may be summed 

 up in a very few words : A great part of its constituents is evidently derived from the 

 blood, and the relations of these principles to nutrition are not understood. The same 

 may be said of sugar, also a constant constituent of the lymph, the origin of which, even, 

 is not known. Urea and, perhaps, other excrementitious matters are taken up from the 

 tissues by the lymph, and are discharged into the blood, to be removed by the appropriate 

 organs from the system. 



While the blood is evidently the great nutritive fluid of the body, being constantly 

 regenerated and purified by the absorption of nutritive matters, by respiration, and by the 

 action of excreting organs, the lymph has an important function in removing from the 

 tissues some, at least, of the products of physiological decay of the organism. 



Chyle. 



During the intervals of digestion, the intestinal lymphatics and the thoracic duct carry 

 ordinary lymph ; but, as soon as absorption of alimentary matters begins, certain nutritive 

 principles are taken up in quantity by these vessels, and their contents are now known 

 tinder the name of chyle. But little remains to be said concerning this fluid, as we have 



