COMPOSITION AND FORMATION OF LYMPH. 445 



co-workers have brought forward many facts to show that the lymph 

 is controlled as to its amount by the activity of the tissue elements 

 and may be considered as a product of the activity of the tissues, as 

 a secretion, in fact, of the working cells. When the salivary glands, 

 the liver, etc., are in greater functional activity the flow of lymph 

 from them is increased beyond doubt, so that the activity of the 

 organs does influence most markedly the production of lymph. 

 Most physiologists, however, prefer to explain this relationship on 

 the view suggested by Koranyi, Starling, and others, namely, that 

 in the metabolic changes of functional activity the large molecules 

 of protein, fat, etc., are broken down to a number of simpler ones, 

 the number of particles in solution is increased and therefore the 

 osmotic pressure is increased. By this means it may be supposed 

 that the flow of lymph toward the tissue elements is increased in 

 proportion to their activity. 



The lymph in the tissue spaces between the cells is subjected 

 to many influences w r hich, taken together, regulate its amount. 

 It is continually augmented by a flow of water and dissolved 

 substances from the blood in the capillaries and from the liquid 

 in the interior of the cells, and it is continually depleted by 

 the excess passing off into the -lymphatics, on the one hand, 

 through which it eventually reaches the blood, and also by direct 

 absorption into the blood capillaries. In regard to this last factor, 

 there is abundant evidence that solutions injected into the tissue 

 spaces so as to increase the amount or concentration of the tissue 

 liquid are promptly absorbed into the blood. The play of these 

 opposing forces maintains the tissue lymph within normal limits, 

 and, although the movement of the water and dissolved sub- 

 stances can not be shown in all cases to be governed solely by 

 the physical processes of diffusion, osmosis, and nitration, there 

 is at present no conclusive evidence that these factors are in- 

 sufficient to account for the regulation. 



Summary of the Factors Controlling the Flow of Lymph. 

 We may adopt, provisionally at least, the so-called mechanical theory 

 of the origin of lymph. Upon this theory the forces in activity are, 

 first, the intracapillary pressure tending to filter the plasma through 

 the endothelial cells composing the walls of the capillaries; second, 

 the force of diffusion depending upon the inequality in chemical 

 composition of the blood-plasma and the liquid outside the capil- 

 laries, or, on the other side, between this liquid and the contents of 

 the tissue elements; third, the force of osmotic pressure. These 

 three forces acting everywhere control primarily the amount and 

 composition of the lymph; but still another factor must be con- 

 sidered ; for when we come to examine the flow of lymph in different 

 parts of the body striking differences are found. It has been shown, 



