526 PHYSIOLOGY CHAP. 



peptone, extract of crab's muscle, etc., alter the composition of the 

 blood, making it more permeable and rendering it incoagulable ; 

 but Cohnstein has demonstrated experimentally that it undergoes 

 such modifications in its chemical constitution as to reduce its 

 endosmotic equivalent very considerably, this being the reason 

 why the amount of lymph increases, and with it the lymphatic 

 current. 



The doctrine of transudation (which results from a combina- 

 tion of the process of filtration with that of diffusion) is thus 

 adequate to explain all the phenomena of the formation of lymph 

 under various experimental conditions, and to render the 

 hypothesis of the secretory functions of the capillary cells super- 

 fluous. Of course this theory does not exclude the possibility that 

 these cells may under abnormal conditions suffer chemical or 

 'physical changes which induce modifications in the normal forma- 

 tion of lymph, since both filtration and diffusion are known to 

 depend upon the constitution of the permeable animal membranes. 

 In a word, it is not denied that the living cells of the capillary 

 walls are the seat of incessant changes corresponding with the 

 degree and kind of their metabolism. What is denied, as being 

 superfluous and non-proven, is that they fulfil a secretory function 

 properly so-called, and that the substances secreted from the blood 

 in the lymphatic spaces differ specifically according to the specific 

 needs of the several tissues and organs. 



The latest work on this subject by Lazarus Barlow, Hamburger, 

 and Asher tends to show that the role of filtration in lympha- 

 genesis must be less than that of the osmotic processes (diffusion), 

 while the relative permeability of the cells of the individual tissues 

 is undoubtedly of importance (Ellinger). Asher and his pupils, in 

 particular, have studied the influence of the activity of cell 

 metabolism in the several tissues on the formation of lymph. 



Another series of experimental observations, made recently by 

 Carlson, Greer, and Luckhardt (1907-10), is of some interest in the 

 problem of the mechanism of lymph formation. Here we can 

 only state briefly that in a large number of experiments (seventeen 

 horses and five dogs) the chloride content of the lymph was found 

 higher than that of the blood serum ; this statement is confirmed 

 by the fact that lymph is a better electrical conductor than serum. 

 A ten per cent increase in the Nad content of a physiological 

 saline solution causes an increase in the electrical conductivity 

 which is comparable to the increased conductivity of the lymph 

 over the serum (Luckhardt). These facts do not agree with any 

 mechanical theory of lymph formation, whether the filtration or 

 the osmosis theory. According to the former, the quantitative 

 salt content of both lymph and serum ought to be the same ; 

 according to the latter it ought to be maintained constant. 



Pugliese (1901) investigated the influence of the vasomotor 



