304 LYMPH. 



may contain more of injected substances than the blood-plasma, 

 while at the same time there is no increase in blood-pressure. 

 From these experiments Heidenhain formed the opinion that 

 filtration and diffusion cannot explain all the facts connected with 

 the formation of lymph, but that it is to be attributed to a selective 

 power of the endothelial cells of the walls of the capillaries, and 

 that lymphagogues act by stimulating these cells. 



This subject has been investigated by Starling, who finds many 

 reasons for upholding the theory of Ludwig as against that of 

 Heidenhain. For a full discussion of the subject we must refer 

 our readers to Schafer's Physiology, but it will not be out of place 

 to quote Starling's conclusions. He says : 



" Thus a renewed investigation of the facts discussed by Heiden- 

 hain has shown that they are not irreconcilable with the filtration 

 hypothesis, but rather serve to support it. At the same time they 

 prove the extreme importance of the factor upon which so much 

 stress was laid by Cohnheim, namely, the nature of the filtering- 

 membrane. In fact, we may say that the formation of lymph and 

 its composition, apart from the changes brought about by diffusion 

 and osmosis between it and the tissues it bathes, depend entirely 

 upon two factors : 1. The permeability of the vessel- wall. 2. The 

 intracapillary blood-pressure. 



" So far as our experimental data go, we have no sufficient 

 evidence to conclude that the endothelial cells of the capillary 

 walls take any active part in the formation of lymph. It seems 

 rather that the vital activities of these cells are devoted entirely 

 to maintaining their integrity as a filtering-membrane, differing in 

 permeability according to the region of the body in which they 

 may be situated. Any injury, whether from within or without, 

 leads to a failure of this their one function, and therefore to an 

 increased permeability, with the production of an increased flow 

 of a more concentrated lymph. 



"We have no evidence that the nervous system has any in- 

 fluence on the production of lymph in any part, except an indirect 

 one by altering the capillary pressures in the part through the 

 intermediation of vasoconstrictor or dilator fibers. This action is 

 better marked in situations where the capillaries are normally 

 very permeable or where the permeability has been increased by 

 local injury to the vessels, or by the circulation of poisons in the 

 blood -stream." 



The lymph-corpuscles enter the lymph as it passes through the 

 lymphatic glands or other lymphoid tissue, such as the tonsils and 

 the thymus gland, and become constituents of the lymph. 



Office of the Lymph. The lymph after it passes out from 

 the blood-vessels bathes the tissues, and is one of their sources of 

 nutrition, but not the only one, for there is abundant evidence that 

 tissues may receive their nutritive supply directly from the blood 

 and pass into that fluid their waste-products. This muscles will 



