t 



220 TEXT-BOOK OF PHYSIOLOGY. 



products will in all probability not only change its normal composi- 

 tion, but also the relative amounts of its normal constituents. 



Chemic analysis has shown that the lymph from the thoracic duct 

 contains from 3.4 to 4.1 per cent, of proteids (serum-albumin, fibrin- 

 ogen), 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 mag- 

 nesium salts. ^Fibrinogen is seldom present beyond o.i per cent., 

 which will account for the feeble and slow coagulation.H Lymph 

 contains both free oxygen and carbon dioxio^\ Of the former, how- 

 ever, 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 indicates 

 that lymph resembles blood-plasma in the character of its constitu- 

 ents, though their relative quantities vary considerably. \\With the 

 exception that it contains no red corpuscles, lymph may be regarded 

 as a diluted" blood. ^ 



Production of Lymph. Though blood is the common reser- 

 voir 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 

 through the capillary wall and is received into the tissue spaces, 

 where it comes 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 and nitra- 

 tion are sufficient to account for all the phenomena. It is assumed 

 that the capillary wall, being an animal membrane, is freely per- 

 meable to water and crystalloid bodies generally; less so, however, 

 to colloid bodies, such as the proteids of the blood-plasma; moreover, 

 that the physiologic conditions of the capillary walls are such as to 

 permit^of a diffusion from the blood to the tissues and the reverse, 

 according to laws similar at least to those determining the passage 

 of substances through animal membranes as determined experiment- 

 ally. The force giving rise to nitration is the difference between the 

 pressure exerted by the blood within the capillary vessels and the 

 pressure exerted by the fluid in the tissue spaces, any increase or de- 

 crease of this pressure being attended by an increase or decrease in 

 the production of lymph. Thus compression of the veins of a part 



