CHAPTER XVII 



THE PRODUCTION OF LYMPH 



BETWEEN the capillaries and the tissue elements is a system of 

 intercommunicating spaces filled with tissue fluid. These inter- 

 stitial spaces are in direct communication with a system of 

 overflow vessels, the lymphatics, which in turn empty them- 

 selves into the otherwise closed vascular system. 1 



The tissue fluid is ultimately derived and replenished from 

 the blood in the capillaries. From it the tissue elements take 

 up the materials necessary for their various anabolic processes, 

 and to it they return the products of their katabolism. 



The problem to be discussed is how this interchange of 

 material between the blood and the tissues is carried on across 

 the fluid in the tissue space. 



We shall first consider the experimental evidence, showing 

 the means by which material may be made to pass to and 

 from the tissue fluid, processes which are called briefly lymph 

 formation and absorption. Having thus ascertained the possible 

 factors at work, we shall consider how the nutrition of the tissues 

 is normally subserved by the tissue fluid in other words, how 

 the tissue fluid is regulated both in quantity and composition 

 according to the needs of the tissue cells. 



It is obvious that tissue fluid might have a second function 

 to perform. It might give up and take from the blood material, 

 and so aid the excretory glands in regulating the volume and 

 composition of the circulating blood. This function will be dealt 

 with incidentally. 



The elucidation of these problems is from the outset fraught 

 with the fundamental difficulty that we cannot collect tissue 



1 It is assumed for simplicity throughout this article that the lymphatics 

 form an open and not a closed system of vessels. The point is at present one of 

 uncertainty. If the system is closed, tissue fluid in order to reach a lymphatic 

 vessel would have to pass through the endothelium of the lymphatic. 



588 



