PKOPERTIES AND FORMATION OF LYMPH 237 



The data pertaining to the humors of the eye, and to the fluid in the 

 endolymphatic and perilymphatic spaces of the internal ear, are not 

 essentially different from those just given. The former have been 

 proved to be true secretory products of the cells covering the ciliary 

 body. Their function is to set up a pressure which keeps the different 

 constituents of the eyeballs in a condition of tension and thus permits 

 of the most perfect refraction of the light rays. The pericardial 

 fluid is clear, yellowish in color, and sticky in character. It contains 

 2.3 to 4.5 per cent, of solids and does not clot spontaneously. Its 

 content in salts (0.76 to 0.87 per cent.) is made up largely of sodium 

 chlorid. The synovial fluid of the joints which, however, cannot be 

 classified as a true transudate, possesses in general the same composi- 

 tion and characteristics as the general lymph, but contains in addition 

 an appreciable amount of mucin. 



The Sources of Lymph. — Volkmann^ has shown at an early date 

 that the principal constituent of the body is water. Upon the basis 

 of two-thirds of water and one-third of solids, an individual weighing 

 60 kilos may be said to contain 40 liters of water; and furthermore, 

 since it has been established by Starling^ that only about 100 c.c. of 

 lymph are returned to the blood in the course of one hour (dog), a very 

 large part of it must be held in the tissues. Only J^go P^^^ of the total 

 quantity of lymph reenters the blood in the time- specified. 



About 70 per cent, of the fluids of the body are contained in the 

 muscles, bones and skin. This statement, however, does not imply 

 that these structures give rise to a proportional amount of intravascular 

 lymph; indeed, it has been found by Starling that the ductus thoracicus 

 derives its contents largely from the abdominal organs which, under 

 ordinary conditions, give lodgment to only about 7 per cent, of the 

 total body-fluid. Practically no lymph is returned from the posterior 

 extremities. It must be evident, therefore, that certain parts of the 

 body contain considerable quantities of fluid, but permit only a small 

 portion of it to escape into the central lymphatic channels. Others, 

 again, are relatively poor in fluid, because they permit a free through 

 flow. It is also true that an organ which gives rise to large quantities 

 of intravascular lymph, generally furnishes a fluid possessing a high 

 specific gravity. Thus, it has been ascertained that the lymph derived 

 from the extremities is very poor in organic material, while that of the 

 liver is rich in these complex substances. The lymph furnished by 

 the other abdominal organs, is not quite so concentrated as the latter. 



The Formation of Ljrmph. — ^Lymph is commonly regarded as 

 diluted blood plasma, i.e., as blood plasma which in its passage through 

 the lining cells of the capillaries has lost some of its coarser constitu- 

 ents. Two theories are held regarding its formation. The oldest 

 of these is the one advocated by Ludwig and his pupils, and modified 

 more recently by Starling. It holds that lymph is formed in a purely 



1 Verh. d. sachs. Ges. der Wissensch., Leipzig, xxvi, 1874. 



2 Schafer's Textbook of Physiology, i, 285, London, 1898. 



