368 ABSORPTION. 



sanguinis effused for the nutrition of the tissues, or from 

 the fluid with which the tissues are kept moist, or, in part 

 also, from degenerated or used portions of the tissues, 

 cannot yet with certainty be determined. Parts which, 

 having entered into the composition of a tissue, and having 

 fulfilled their purpose, require to be removed, may not be 

 altogether excrementitious, but may admit of being re- 

 organized and adapted to the nutrition of the same or 

 some lower tissue ; and these may be absorbed by the 

 lymphatics. On the whole, however, it is most probable 

 that the lymph is derived in great part, from the liquor 

 sanguinis; since changes in the character of the former 

 usually correspond very closely with changes in the charac- 

 ter of either the whole mass of blood, or of that in the 

 vessels of the part from which the lymph is examined. 

 Thus Herbst found that the coagulability of the lymph is 

 directly proportionate to that of the blood ; and that when 

 fluids are injected into the blood-vessels in sufficient 

 quantity to distend them, the injected substance may be 

 almost directly afterwards found in the lymphatics. 



Lymph-Hearts. In reptiles and some birds, an important 

 auxiliary to the movement of the lymph and chyle is sup- 

 plied in certain muscular sacs, named lymph-hearts (fig. 96), 

 and Mr. Wharton Jones has lately shown that the caudal 

 heart of the eel is a lymph-heart also. The number and 

 position of these organs vary. In frogs and toads there 

 are usually four, two anterior and two posterior ; in the 

 frog, the posterior lymph-heart on each side is situated in 

 the ischiatic region, just beneath the skin j the anterior 

 lies deeper, just over the transverse process of the third 

 vertebra. Into each of these cavities several lymphatics 

 open, the orifices of the vessels being guarded by valves, 

 which prevent the retrograde passage of the lymph. From 

 each heart a single vein proceeds and conveys the lymph 

 directly into the venous system. In the frog, the inferior 

 lymphatic heart, on each side, pours its lymph into a 



