ABSORPTION. 221 



which interferes with the outflow of blood from the capillaries, or a 

 dilatation of the arterioles which increases the inflow of blood, will 

 increase both the capillary pressure and the production of lymph. 

 The reverse conditions will, of course, diminish lymph production. 

 Hemorrhages which lower the general blood-pressure may so lower 

 the capillary pressure as not only to stop the flow to the tissues, but 

 give rise to a diffusion current from the tissues into the blood. 



The quantitative composition of the lymph compared with that 

 of the blood indicates that it is produced by diffusion and nitration. 

 In the lymph the concentration of the inorganic salts is practically 

 the same as in the blood ; the concentration of the proteids, however, 

 is somewhjitjggs^ These facts are 111 a&}F9&!UH! With what is known 

 regarding the diffusibility of both crystalloids and colloids through 

 animal membranes. 



According to other investigators, the production of lymph is not 

 so much due to intracapillary pressure as it is to the specialized 

 activities of the endothelial cells, activities which indicate that lymph 

 is a secretion the composition of which varies in different situations 

 in virtue of a difference in the molecular structure of the endothelial 

 cells. As is the case with many of the secreting cells of the body, 

 the injection of various substances into the blood apparently increases 

 the activity of the endothelial cells, as shown by an increased lymph 

 production without any appreciable increase of intracapillary pressure. 

 Thus it has been shown that after the injection into the blood of 

 sugar, sodium chlorid, sodium sulphate, urea, etc., there is an increase 

 in the flow of lymph from the thoracic duct. The lymph, however, 

 under these circumstances is richer in water than normally. As the 

 blood at the same time increases its percentage of water, it is 

 assumed that the water is extracted from the tissues, by reason of an 

 increased percentage of salts in the tissue spaces due to increased 

 activity of the endothelial cells. A higher percentage of salts in the 

 lymph than in the blood is difficult to account for on the diffusion- 

 filtration theory. The injection of peptones, albumin, the extract 

 of the muscles of the leech, crab, mussel, etc., is also followed by an 

 increase in the amount of lymph discharged from the thoracic duct; 

 but in this instance the lymph possesses a higher degree of concen- 

 tration, being richer not only in inorganic but also organic constit- 

 uents. The cause of this increase in both the quantity and quality 

 of the lymph is believed to be an increased activity in the secreting 

 power of the endothelial cells. It is possible that all these facts may 

 be otherwise interpreted; the subject is yet a matter of investigation. 



Functions of Lymph. The lymph, from its situation, its rela- 

 tion to the tissues, and its composition, must be regarded as thejouxce 

 of the nutritive material from which the tissues derive those sub- 

 stances necessary for their growth and repair, as well as for the 



