The peculiar property by which the minute lacteal vessels imbibe or take up the white chyle is not well understood. From the fact in physics that liquids rise in capillary tubes, the inference has been drawn that absorption in living vessels also takes place from capillary attraction. But in the animal body the application of the principle is undoubtedly modified by the properties peculiar to organization, and one of the most remarkable proofs of this is the circumstance of the absorbent vessels in different situations having to some extent a specific adaptation to the qualities of the substances upon which they are severally destined to act. At one time, indeed, it was supposed that the principle of exclusive adaptation was so complete that every absorbent vessel was permanently shut to every thing except its own peculiar object, and that, from amidst many elements, each selected its own with unerring tact. But of late it has been proved that the absorbents are less rigidly discriminating than was previously supposed, and that substances are readily taken up by them which Nature never intended them to receive. In mixing madder with the food of fowls, for example, for the purpose of dyeing their bones, the colouring matter of the root is taken up without difficulty by the absorbents along with the chyle, although madder was certainly never intended to be their natural stimulus. But even admitting this latitude in its fullest extent, there still exist a fitness and peculiarity of relation between the absorbents and their _proper_ objects, which renders the latter more accessible to them than to any foreign body. The lacteal vessels are most easily seen an hour or two after a meal; because they are then fully distended with chyle, even in their smaller branches. The latter, indeed, may then be distinctly traced proceeding from the different portions of intestine, and gradually coalescing into larger trunks, as seen at LL in the figure on p. 163. These, again, terminate in the vessel called the thoracic duct (the beginning of which is seen at TD in the same figure), by which the chyle is conveyed almost in a direct course along the spine, and which is represented at DDDD in the annexed cut. On its arrival at the upper part of the chest, the thoracic duct crosses over and opens into the subclavian vein S, just before the latter reaches the right side of the heart, so that the chyle is there poured into the circulating current of the _venous_ blood. [Illustration]