This section is from the book "Animal Physiology: The Structure And Functions Of The Human Body", by John Cleland. Also available from Amazon: Animal Physiology, the Structure and Functions of the Human Body.
The Lymphatics commence in very fine networks, and in interstitial spaces in the tissues; in some instances lined with exceedingly delicate epithelium, like the capillary blood-vessels, and in others not. The fluid which they contain is termed lymph. The lymph is a clear, transparent fluid, slightly alkaline in reaction, as is the blood, and containing albumen, salts, and a variable amount of extractive. As it comes from the tissues it is perfectly structureless; but, after passing through lymphatic glands, it contains lymph corpuscles identical in all respects with the white corpuscles of the blood, and also becomes spontaneously coagulable, forming a weak clot. The function of the lymphatic glands appeal's, therefore, to be to form white corpuscles; and this view is corroborated by their structure: for the lymphatics, on entering them, lose their proper walls, and are continued into irregular spaces, winding between masses of stroma loaded with corpuscles which, as they develop, are loosened, and float away in the lymph. The addition of the corpuscles to the lymph is sufficient to account for its acquiring the property of coagulability; the reason for the lymph, as it comes from the tissues, not being spotaneously coagulable, being simply that, like liquor sanguinis drawn pure from the vein (p. 110), it contains no flbrinoplastin.