VITALISM. 31 



measurements of pressures and of solubilities leave no 

 doubt in this respect. The living elements of the 

 pulmonary membrane must therefore intervene in 

 order to disturb the physical phenomenon. Things 

 happen as if the exchanged gases were subjected not 

 to a simple diffusion, a physical fact obeying certain 

 rules, but to a real secretion, a physiological or vital 

 phenomenon, obeying laws which are also fixed, but 

 different from the former. 



On the other hand, Heidenhain was led about the 

 same time to analogous conclusions with respect 

 to the liquid exchanges which take place within 

 the tissues, between the liquids (lymphs) which 

 bathe the blood-vessels externally and the blood 

 which those vessels contain. The phenomenon is 

 very important because it is the prologue of the 

 actions of nutrition and assimilation. Here again, 

 the two factors of exchange are brought into relation 

 through a thin wall, the wall of the blood-vessel The 

 physical laws of diffusion, of osmosis, and of dialysis, 

 enable us to foretell what would take place if the 

 vitality of the elements of the wall did not intervene. 

 Heidenhain thought he observed that things took 

 place otherwise. The passage of the liquids is dis- 

 turbed by the fact that the cellular elements are aliire. 

 It assumes the characteristics of a physiological act, 

 and no longer those of a physical act Let us add 

 that the interpretation of these experiments is difficult, 

 and it has given rise to controversies which still 

 persist. 



These two examples, around which others might be 

 grouped, have led certain physiologists to diminish the 

 importance of the physical factors in the functional 

 activity of the living being to the advantage of the 



