LYMPH FORMATION 605 



metabolism in the animal body or in an animal cell is disintegra- 

 tion, a breaking down of large complex unstable molecules of high 

 potential energy into a great number of small simple stable mole- 

 cules of small potential energy, the total output of an animal cell 

 must have a higher osmotic pressure than the total income, so 

 that all the metabolic changes in the tissues would tend to increase 

 the osmotic pressure of the lymph with which they are bathed.' ' 

 This increased osmotic pressure of the tissue fluid would lead to 

 a flow of water from the blood into the tissue spaces, and so to 

 an increased flow along the lymphatic vessels. 



Asher, however, seems rather to favour the second possibility, 

 namely, that lymph during tissue activity is formed by a process 

 analogous to a secretion. That is to say, a gland cell when active 

 turns out its specific secretion into its duct on one side and lymph 

 into a tissue space on the other. His reason for adopting this view 

 was his observations on the parallelism of the flow of lymph and 

 saliva post-mortem, already referred to. He concluded that both 

 phenomena are due to the same forces, and that since the pour- 

 ing out of saliva is a secretion, so must also be the formation of 

 lymph. This, however, does not necessarily follow ; even suppos- 

 ing both phenomena are due to the same forces, it may equally 

 well be that diffusion and osmosis cause the lymph flow and are 

 also of great importance in this post-mortem gland secretion. A 

 phenomena somewhat similar to this post-mortem salivary secretion 

 has been observed by Mathews. If the blood supply is cut off for 

 twenty-five minutes from the sub-maxillary gland and then re- 

 admitted, a marked vaso-dilatation takes place, and the gland 

 secretes rapidly. He accounts for this by increased osmotic 

 pressure within the cells. 



Tissue activity may be held to increase lymph flow, in part 

 at any rate, by raising the osmotic pressure of the tissue fluid ; 

 and this must be especially marked during proteid metabolism. 

 For proteids have at most a minute osmotic pressure. And 

 when the cell takes them up from tissue fluid it will not thereby 

 materially decrease the osmotic pressure of that fluid, but by 

 returning a number of smaller stable molecules it will greatly 

 increase the osmotic pressure of tissue fluid and lymph. We 

 should therefore expect to find that during tissue metabolism 

 the osmotic pressure of the lymph would tend to keep above 

 that of the blood. And this Leathes has found to be the case. 



