The nature and use of the lymph have, I believe, never been perfectly ascertained; but it is supposed to consist of matter that has been previously animalised, and which, after answering the purpose for which it was intended, must, in regular rotation, make way for the fresh supplies produced by nourishment. The lymphatic vessels pump up this fluid from every part of the system, and convey it into the veins to be mixed with the blood which runs through them, and which is commonly called venous blood. CAROLINE. But does it not again enter into the animal system through that channel? MRS. B. Not entirely; for the venous blood does not return into the circulation until it has undergone a peculiar change, in which it throws off whatever is become useless. Another set of absorbent vessels pump up the _chyle_ from the stomach and intestines, and convey it, after many circumvolutions, into the great vein near the heart. EMILY. Pray what is chyle? MRS. B. It is the substance into which food is converted by digestion. CAROLINE. One set of the absorbent vessels, then, is employed in bringing away the old materials that are no longer fit for use; whilst the other set is busy in conveying into the blood the new materials that are to replace them. EMILY. What a great variety of ingredients must enter into the composition of the blood? MRS. B. You must observe that there is also a great variety of substances to be secreted from it. We may compare the blood to a general receptacle or storehouse for all kinds of commodities, which are afterwards fashioned, arranged, and disposed of as circumstances require. There is another set of absorbent vessels in females which is destined to secrete milk for the nourishment of the young. EMILY. Pray is not milk very analogous in its composition to blood; for, since the nursling derives its nourishment from that source only, it must contain every principle which the animal system requires? MRS. B. Very true. Milk is found, by its analysis, to contain the principal materials of animal matter, albumen, oil, and phosphat of lime; so that the suckling has but little trouble to digest and assimilate this nourishment. But we shall examine the composition of milk more fully afterwards. In many parts of the body numbers of small vessels are collected together in little bundles called _glands_, from a Latin word meaning acorn, on account of the resemblance which some of them bear in shape to that fruit. The function of the glands is to _secrete_, or separate certain matters from the blood.