COMPOSITION AND PROPERTIES OF THE CHYLE AND LYMPH. 455 



cordance with the emptiness of the Absorbent system, which usually presents 

 itself in Man some little time after death. Hence it seems probable that regular 

 propulsion of the fluid during life may be effected by alternate contractions and 

 dilatations of successive portions of the vessels, slowly repeated at intervals. 1 

 There are, however, certain auxiliary forces. For, in the first place, a part of 

 the movement may be attributed to the vis a tergo, which is produced by the 

 continual introduction of fresh fluid into the rootlets, so to speak, of the vascu- 

 lar tree ; and this more especially in the case of the lacteals, since the muscularity 

 of the villi seems to enable them to act as so many minute force-pumps, whereby 

 the fluid which they have- imbibed may be impelled onwards ( 460). It may 

 be thought that, from the extreme distensibility of the walls of the absorbents, 

 this force would be rather expended in dilating them, than in pushing on the 

 current of liquid which they contain ; but it must be borne in mind that they 

 are for the most part closely surrounded with tissues which exert a certain degree 

 of pressure upon them, and that this is much greater during life than after 

 death. Further, in all the movable parts of the body, assistance is doubtless 

 afforded (as it is to the circulation in the Veins, CHAP. ix. SECT. 4) by the oc- 

 casional pressure exercised upon the Absorbents by the surrounding tissues ; for 

 while this pressure is operating it will tend to empty them of their contents, 

 which are only permitted by their valves to pass in one direction ; and when the 

 pressure is relaxed, they will be refilled from behind. 



480. It seems obvious, from what has been stated, that we are to regard the 

 entire Absorbent system as a great blood-making gland ( 473), designed to 

 exert a certain power of conversion or vitalization over the matters which enter 

 it, either from the alimentary canal or from the body in general. In the case 

 of the Lacteal portion of the system, there seems to be a strong indication that 

 one part of the converting process consists in the intimate admixture which the 

 albuminous constituent of the chyle undergoes with its fatty constituent, owing 

 to the subdivision of the latter, and its diffusion through an albuminous fluid. 

 And the effects of this admixture are peculiarly shown by the tenacity with 

 which fat is incorporated with albumen and fibrin ( 20, 25), so that it is dif- 

 ficult to separate them ; this incorporation, it seems probable, having a peculiar 

 reference to the very first process of cytogenesis, in which molecules of fatty 

 matter seem always to be present in close collocation with albuminous particles 

 ( 42). As already pointed out, the "plasticity" of the different albuminous 

 compounds holds such a direct relation to the quantity of fat they contain 

 (within certain limits), that we can scarcely help looking at this incorporation 

 as one of the most important parts of the assimilating process. And thus it 

 seems to be, that the presence of fatty matters in the food is essential to healthy 

 nutrition ( 404, in.); for no production of fat by the agency of the liver can 

 bring the raw albumen into the same intimate relationship with the minutely- 

 divided fatty molecules. What other changes the fluid of the lacteals may 

 undergo, in addition to the production of fibrin and of corpuscles which has 

 been already noticed, and what is the special purpose of the elaboration to which 

 the fluid of the Lymphatics is subjected, cannot as yet be distinctly stated. 

 Probably, however, the changes in question are less of a chemical than of a vital 

 nature, and are such as serve to prepare the fluid for maintaining the vital acti- 

 vity of the several parts of the organism to which it is to be distributed. 



x A regular rhythmical movement of the veins of the Bat's wing, obviously dependent 

 upon their independent contractility, has lately been observed by Mr. Wharton Jones 

 (" Proceedings of the Royal Society," Feb. 5, 1852). The existence of such a movement 

 in the Veins of a part, as an auxiliary propulsive force, obviously strengthens the proba- 

 bility of its occurrence in the Lymphatics, as the principal propelling power, where no 

 central impulsive organ exists ; just as a like movement is seen in the bloodvessels of 

 such of the lower Invertebrata as have no heart. 



