(ABSORPTION BY THE LYMPHATICS. 285 



gine, that this effete matter would be mingled with the newly-ingested 

 aliment, and would be poured back with it into the general current of 

 the circulation, instead of being at once carried out of the system. And 

 the idea is directly negatived, as we shall presently see, by the actual 

 composition of the lymph drawn from these vessels ; the solid matter of 

 which consists, in great part at least, of substances of a nutritive cha- 

 racter. It is true that other substances are occasionally found in the 

 lymphatics ; thus, when the gall-bladder and bile-ducts are over-dis- 

 tended with bile, in consequence of some obstruction to its exit, the 

 lymphatics of the liver are found to contain a biliary fluid. In like 

 manner, the lymphatics in the neighbourhood of a large abscess have 

 been found to contain pus. When the limb of an animal, round the 

 upper part of which a bandage is tied, is kept for some hours in tepid 

 milk, the lymphatics of the skin are found distended with that fluid. 

 And when saline solutions are applied to the skin, they are usually 

 detected more readily in the lymphatics, than in the veins. But these 

 facts only prove, that the lymphatics very readily imbibe soluble sub- 

 stances with which they are in proximity ; and this imbibition seems to 

 take place on the same physical principles, as the imbibition of soluble 

 substances by the veins of the intestinal canal. 



503. The more ready absorption of such substances by the lympha- 

 tics, than by the veins, of the cutaneous surfaces, contrary to what 

 obtains in the alimentary canal, is easily accounted for, by the very 

 abundant distribution of the lymphatics in the skin, and the ready- 

 access which fluids can obtain to their walls. In other tissues it is 

 different : thus it appears that saline matters injected into the lungs 

 are detected much sooner in the serum of the blood, than they are in 

 the lymph ; and make their appearance earlier in the left cavities of 

 the heart, to which they would be conveyed by the pulmonary vein, 

 than in the right, which they would reach through the thoracic duct 

 and descending cava. This is obviously due to the minute distribution 

 of the blood-vessels upon the walls of the air-cells ; which makes them 

 far more ready channels for the imbibition of fluid, than the lym- 

 phatics could be. In regard to the occasional absorption of pus from 

 the cavity of an abscess or of an open ulcer, by the lymphatics, it is to 

 be remarked that the absorbent vessels must themselves probably be 

 laid open by ulceration ; since in no other way can we understand the 

 entrance of the globules, so large as those of pus, into their interior. 



504. In regard to the cause of the movement of the chyle and lymph 

 along the absorbent vessels, from their commencement to their termina- 

 tion in the central receptacle, no very definite account can be given. 

 The middle coat of these vessels has a fibrous texture ; and the fibres 

 bear some resemblance to that of the non-striated muscle. In the 

 thoracic duct, this fibrous structure is more evident; and. distinct con- 

 tractions have been excited in it, by irritating the sympathetic trunks 

 from which it receives its nerves, and the roots of the spinal nerves with 

 which those trunks are connected. Hence it seems probable, that there 

 is a sort of peristaltic contraction of the wUlls of the absorbents, 

 analogous to that which takes place in the intestinal tube, serving to 

 drive their contents slowly onwards ; their reflux being prevented by 



