590 EXPERIMENTS DEALING WITH 



EXPERIMENTS DEALING WITH LYMPH FORMATION 



The method of investigating normal lymph formation is neces- 

 sarily experimental. Although we classify all such experiments as 

 physiological, it must be remembered that many of them are 

 just as pathological as those which occur in the body as the 

 result of disease. It is clear that tissue fluid is always being 

 formed and absorbed in the body, and we wish to find out how 

 and in response to what this process is carried out. In order 

 to do this with certainty, our experiments should, if possible, 

 reproduce conditions which are normal to the healthy body. 

 Such experiments are truly physiological. The same, however, 

 cannot be said of many of the earlier experiments dealing 

 with this subject. They brought to light a number of factors 

 which can alter lymph formation, but under experimental con- 

 ditions which were highly abnormal. For instance, the injection 

 of leech extract into a dog increases the lymph flow along 

 the thoracic duct. This is a wholly abnormal condition, and 

 it does not follow that the factors involved play any part in 

 normal lymph formation. The first thing to be decided is, under 

 what physiological conditions in the body is the formation of 

 lymph altered. And then to discuss by what process or factors 

 this alteration is brought about. 



The answer to the first question has been given by the work 

 chiefly of Asher and his pupils. 



Asher' s view was first published in 1897. He maintains 

 that lymph in a lymphatic vessel is a product of the activity 

 of tissue cells and independent of blood pressure. The immediate 

 cause of increased lymph flow is to be looked for in an increase 

 of the metabolism or specific activity of cells, and according to 

 the intensity of this activity the quantity and concentration of 

 the lymph will alter. 



Asher draws a sharp distinction between tissue fluid and 

 lymph in a lymphatic vessel. Tissue fluid is derived from 

 the blood and carries nutriment to the tissues : it also receives 

 katabolic products of cell activity. Of these products some are 

 non-poisonous and pass back direct into the capillary ; others, 

 however, are poisonous, are removed from the tissue spaces 

 in solution as lymph, and in their passage through lymph 



