190 THEORETICAL DEDUCTIONS 



membrane. All these particles form more or less dense 

 agglomerations, are immersed in a clear liquid composed of 

 salts and crystalloids. The cells themselves are immersed 

 in a liquid which is composed of the same salts and crystal- 

 loids, and which in addition contains colloidal particles 

 (plasma, lymph, etc.). 



From the point of view of the nutrition of intracellular 

 particles, we distinguish in the organism three zones or media 

 through which nutritive substances must pass. 



These zones or media are separated from each other by 

 dialysing membranes which function by virtue of their 

 density, and by virtue of the differences in tonicity of the 

 liquids on either side of the membrane, and especially by 

 virtue of the chemical affinities between the components of 

 the membrane and of these liquids. 



The organism as a whole begins by making a first choice 

 of the substances needed for its nutrition from the first 

 external medium. A second choice is made by the mem- 

 branes of the digestive tract which allow to pass into the 

 blood only certain selected substances which have been 

 transformed into simple compounds. A third choice is made 

 by the cell-membranes which absorb certain substances 

 and allow the remainder to be eliminated by the kidneys 

 and the intestines. 



In this way, the alimentary substances absorbed by the 

 mouth undergo a series of successive fragmentations and 

 selective passages through the membranes before they, in a 

 crystalloid state, reach the intracellular "micelles," that 

 is the nutrition units. 



A cell may allow certain colloids made up of small "micelles" 

 to penetrate into its interior. If these "micelles" are homo- 

 geneous, that is to say, have the same physico-chemical equili- 

 brium as those which compose the plasma of the cell, the 

 cell may assimilate a certain number without undergoing 

 appreciable change in its own general nutritive equilibrium; 

 but in the case of "micelles" having physico-chemical equili- 

 bria differing from those of the cell " micelles," the nutrition 

 equilibrium of the invaded cell and of the new "micelles" 

 will be disturbed to a greater or less extent. 



