FORMATION OF LYMPH 331 



Chyle differs from lymph chiefly in the presence of large quantities of fat; 

 during starvation the lymph and the chyle are of practically the same composition. 



Normal lymph contains much less fibrinogen than does the blood plasma, and 

 hence coagulates slowly. Lipase and other enzymes have been found in the lymph, 

 as in the plasma. The products of tissue metabolism added to the lymph by 

 the cells may render it toxic (Asher and Barbera'). Under pathological condi- 

 tions the lymph may be greatly altered, becoming poorer in solids under some 

 conditions of edema, and becoming rich in proteins and blood-corpuscles under 

 inflammatory conditions, until it partakes of the characteristics of an inflam- 

 matory exudate (see analyses of transudates and exudates). 



An important fact to consider is, that of the entire water of the 

 body but about one-tenth is in the blood. About two-thirds of the 

 entire weight of the body is water, which is mostly in the cells and 

 tissues, firmly bound by the colloids, only an unknown but smaller 

 portion being as free movable fluid, and even here always associated 

 with more or less colloid. A body weighing 60 kilos will, therefore, 

 have 40 kilos of water, of which but about 4 kilos is blood. 



FORMATION OF LYMPH^ 



Filtration Theory. — The simplest possible conception of lymph 

 formation is that it is merely the result of filtration of the liquid con- 

 stituents of the blood through the capillary walls under the influence 

 of the blood pressure. This "filtration theory" was supported origi- 

 nally by Ludwig, and it was a prominent factor in the early appli- 

 cations of mechanical principles to biological processes. In support 

 of this theory were advanced the results of numerous experiments in 

 which it was shown that increasing the blood pressure by means of 

 ligating the veins, or by causing arterial dilata ion, resulted in an in- 

 ■ crease of the lymph flowing out of the lymph-vessels of the part. 

 Also, when the blood pressure is raised by epinephrine or by other 

 means, a large proportion of the fluid leaves the blood vessels; con- 

 versely, when the blood pressure is suddenly lowered by hemorrhage 

 there is a rapid passage of fluid from the tissues into the blood. The 

 experimental results were not always favorable to the theory, how- 

 ever, particularly in the experiments in which blood pressure was 

 raised by arterial dilatation; often the flow of lymph was Kttle in- 

 creased, even when the arterial flow and pressure were greatly in- 

 creased. iSlevertheless, the filtration theory held for many years, not 

 only as an explanation of lymph formation, but also as an explanation 

 of urinary secretion and of the secretion by other organs. It was 

 only within a comparatively short time that it became clear that filtra- 

 tion alone could not account for all the phenomena of secretion. For 

 example, in many lower forms with undeveloped circulatory systems, 

 and almost no blood pressure, secretion goes on vigorously; the pres- 

 sure of glandular secretions may be much higher than the blood 

 pressure within the capillaries; the activity of secretion is by no means 



2 Zeit. f. Biol., 1898 (36), 154. 



^ See review by Asher, Biochem. Centralblatt, 1905 (4), 1. 



