FORMATION OF LYMPH 279 



the influence of these substances is poorer in proteids than ordi- 

 nary lymph, and at the same time an increased urinary secretion 

 is produced. With these crystalloidal lymphagogues the amount 

 of effect is in inverse proportion to their molecular weight, 

 which means that their effects depend upon the number of 

 molecules in solution rather than upon their nature ; in other 

 words, the stimulation of lymph by crystalloids is dependent 

 upon the osmotic pressure of the crystalloids. Heidenhain 

 explained their action as follows : The crystalloids are secreted 

 into the lymph-spaces by the action of the capillary endothelium, 

 and there, owing to their raising osmotic pressure, cause a flowing 

 of water out of the vessels. The difficulty here is to explain why 

 the crystalloids while still in the vessels do not attract the fluids 

 from the lymph-spaces into the blood, and so cause rather a 

 lessened lymph secretion. 



While admitting that in pathological conditions (e. g., pas- 

 sive congestion) pressure and filtration may play an important 

 part, Heidenhain considered that an active secretion by the 

 endothelial cells is the chief factor in the normal formation of 

 lymph. The means by which the cells perform this function 

 was unknown; it was considered as an example of "vital activ- 

 ity/' Heidenhain meaning by this term such chemical and 

 physical forces of living cells as are unknown or not under- 

 stood at the present time, rather than any metaphysical concep- 

 tion of living matter, such as many vitalists assume. 



Other observers, corroborating Heidenhain' s results for the 

 most part, have modified or amplified his theory. Asher and 

 his collaborators, for example, ascribe the work done in caus- 

 ing lymph formation to the cells of the various tissues and 

 organs, rather than to those of the capillary wall. The 

 increased flow of lymph from the salivary gland that occurs 

 during its activity they consider due to the work of the gland 

 cells, and its function the removal of products of metabolism. 

 The action of such a lymphagogue as peptone they ascribe to 

 its stimulation of cellular activity, particularly in the liver, 

 where it causes an increased formation of bile. Gies 1 and 

 Asher also observed that after injection of crystalloidal lympha- 

 gogues, such as sugar, a prolonged flow of lymph occurred 

 after the death of the animal, proving completely that such 

 lymphagogic action is independent of blood pressure. 



Potocytosis, In explanation of the process by which the cells, 

 whether endothelial or tissue-cells, pass fluids through themselves from 



1 Amer. Jour. Physiol., 1900 (3), p. xix; Zeit. f. Biol., 1900 (40), 207. 



