BLOOD 499 



volume, and after the injection of hypotonic saline and other 

 non-colloidal fluids into the blood-vessels, water passes out 

 into the tissues. The volume of the blood is thus regulated. 



The origin of the proteins is unknown, although 

 ultimately they must come from the food ; very probably 

 they are in part derived from the tissues. But the signifi- 

 cance of the two proteins, albumin and globulin, and of their 

 variations has not yet been elucidated. 



The glucose is derived from the carbohydrates and from 

 the proteins of the food, and during starvation it is constantly 

 produced in the liver and poured mto the blood (p. 354). 



The fats are derived from the fats and carbohydrates of 

 the food and tissues (p. 351). 



The urea and other waste constituents are derived from 

 the various tissues. A transference of sodium phosphate 

 from the tissues to the blood occurs when acidosis is 

 threatened, probably by the dissociated HCl of the NaCl of the 

 blood passing into the cells and turning out the phosphate 

 as NaHoPOi to be excreted (p. 48 2). 



B. Cells — I. Leucocytes. — 1. In the embryo these are first 

 developed from the mesoderm cells generally. In extra- 

 uterine life they are formed in the lymph tissue and in the 

 red marrow of bone. 



2. Lymph Tissue is very widely distributed in the body, 

 occurring either in patches of varying shape and size, or as 

 regular organs, the lymphatic glands (fig. 205). These are 

 placed on the course of lymphatic vessels, and consist of a 

 sponge- work of fibrous tissue, in the interstices of which are 

 set patches of lymph tissue, in which multiplying lymphocj^tes 

 are closely packed together. Each mass of lymphatic tissue 

 is surrounded by a more open network, the sinus, through 

 which the l3^mph flows, carrying away the lymphocytes from 

 the germ centres. In the sinuses are found many cells with 

 a marked phagocytic action, and, when erythrocytes are 

 destroyed by ha^molytic agents, the pigment and the iron 

 derived from the haemoglobin are often found abundantly in 

 the cells in the sinuses of lymph glands. 



Round some of the lymphatic glands of certain animals 

 large blood spaces or sinuses are seen, and these glands are 



