ABSORPTION 215 



from the vessels lymph undergoes a spontaneous coagulation, though 

 the coagulum is never as firm as that observed in the coagulation of the 

 blood. The cause of the coagulation is the appearance of fibrin. After 

 a variable length of time the coagulum separates into a liquid and a solid 

 portion, the serum and the clot. 



The Chemic Composition of Lymph. Although the lymph obtained 

 from the tissue spaces, from the lymph-vessels, as well as from the so-called 

 serous cavities has the same general chemic composition, there is reason 

 for the view that it varies in its ultimate composition according as it is 

 derived from one region of the body or from another. The needs of any 

 individual tissue as well as the character of its metabolic products will 

 in all probability change not only its normal composition, but also the 

 relative amounts of its normal constituents. 



Chemic analysis has shown that the lymph from the thoracic duct con- 

 tains from 3.4 to 4.1 per cent, of proteins (serum-albumin, fibrinogen), 

 0.046 to 0.13 per cent, of substances soluble in ether (probably fat), o.i 

 per cent, of sugar, and from 0.8 to 0.9 per cent, of inorganic salts, of which 

 sodium chlorid (0.55 per cent.) and sodium carbonate (0.24 per cent.) are 

 the most abundant (Munk). There are usually in most specimens small 

 quantities of potassium, calcium, and magnesium salts. Fibrinogen is 

 seldom present beyond o.i per cent., which will account for the feeble and 

 slow coagulation. Lymph contains both free oxygen and carbon dioxid. 

 Of the former, however, there is but a small percentage; of the latter, about 

 45 vols. per cent., partially in the free state and partially combined with 

 sodium. Urea is also present in very small amounts. This analysis indi- 

 cates that lymph resembles blood-plasma in the character of its constituents, 

 though their relative quantities vary considerably. With the exception 

 that it contains no red corpuscles, lymph may be regarded as a diluted 

 blood. 



The Production of Lymph. Though blood is the common reservoir of 

 nutritive material, the latter is not available for nutritive purposes as long 

 as it is confined within the blood-vessels. The capillary wall, thin as it is, 

 and composed of but a single layer of endothelial cells, would be sufficient 

 to prevent its utilization by the tissues, if it were not permeable to the liquid 

 portion of the blood. As this is the case, however, it is found that as the 

 blood flows through the capillary vessels a portion of the blood-plasma 

 passes across the capillary wall and is received into the tissue-spaces, 

 where it conies into intimate contact with the tissue-cells. 



The forces concerned in the passage of the constituents of the blood- 

 plasma across the capillary wall have been the subject of much investigation. 

 According to some investigators, diffusion, osmosis, and filtration are suffi- 

 cient to account for all the phenomena. For a consideration of the phenom- 

 ena of diffusion, osmosis, and filtration the reader is referred to paragraphs 

 at the end of this chapter. It is assumed that the capillary wall, being an 

 animal membrane, is freely permeable to water and crystalloid bodies gener- 

 ally; less so, however, to colloid bodies, such as the proteins of the blood- 

 plasma; moreover, it is further assumed that the physiologic conditions of 

 the capillary walls are such as not only to permit of the passage of the con- 

 stituents of the blood into the tissue spaces, but also the passage of the con- 

 stituents of the intercellular lymph into the blood, according to laws similar 



