THE THEORY OF OSMOTIC PRESSURES. 291 



the absorption of water from the intestines begins to take 

 place long before the osmotic pressure of the fluid has 

 reached that of the blood, and the lowering of the osmotic 

 pressure takes place in consequence of absorption of salt, 

 and not from a pouring out of water. 



From a study of these and many similar experiments 

 Heidenhain concludes that two kinds of processes are at 

 work in intestinal absorption. In the first place, there is 

 the physiological activity of the living cells, which take up 

 probably a fluid of the composition of the intestinal con- 

 tents ; and, in the second place, there is the purely 

 physical force of osmosis, which, according to the com- 

 .position, may aid or subtract from the effect of the cellular 

 activity. The result then is due to the algebraic summa- 

 tion of these two distinct processes, the one physical, the 

 other physiological. 



The physiological factor can be annulled by mixing 

 with the salt solutions minute traces of a poison such as 

 sodium fluoride. By this means the cells are paralysed, or 

 hindered in their activities, and the absorption of water or 

 salt now takes place in the direction determined by the 

 osmotic differences. Magnesium sulphate appears to have 

 a somewhat similar action, but to a much less marked 

 degree. 



Hamburger 1 has employed a somewhat similar argu- 

 ment to prove that lymph cannot be produced by a process 

 of filtration, and that in its production work is done by the 

 endothelial cells of the capillaries. I have pointed out 

 elsewhere" 2 several evident objections to his reasoning, and 

 experiments of my own have shown me that the sooner the 

 lymph is tested after it has left the vessels the closer is its 

 osmotic pressure to that of the blood-plasma, and that the 

 minute difference in osmotic pressures ordinarily observed 

 between blood and lymph is due to the fact that this 

 latter alters the tissue cells in its way to the lymphatics, 



! " Untersuchungen liber die Lymphbildung." Zeitsch. f. Biologie, p. 



' l "The Influence of Mechanical Factors on Lymph Formation."' 

 Journ. of Phys., xvi., p. 266. 



