100 THE NUTRITIVE FUNCTIONS. 



supply of the original fluid, and in this way a continual 

 flow of the fluid in the same direction would be produced. 



Now such appears to be, to a very great extent, the 

 nature of those influences which govern the movements of 

 the nutrient fluid in the capillaries of animals and plants. 

 The fluid, for example, contains certain substances which 

 are necessary to the nutrition of a certain tissue, and it is 

 for this reason attracted into that tissue to which it imme- 

 diately gives up the nutrient elements required ; this neu- 

 tralizes the affinity between the tissue and the fluid, and 

 the latter is consequently driven out by the superior at- 

 traction then possessed by the tissue for a fresh portion of 

 the fluid. The fluid which is driven out of one part may 

 still, however, be qualified to nourish another part which 

 requires a different portion of its elements, and between it 

 and this new tissue an affinity now exists, the result of the 

 loss it has already sustained, which did not exist before; 

 it is thus drawn into the fresh tissue and repelled from it 

 as before, by the entrance of a fresh supply, and in this 

 manner the current moves on from cell to cell, through 

 the entire capillary network. This important physiological 

 law was first developed by Professor Draper 5* and seems 

 to afford a clear and satisfactory explanation of the motion 

 of the nutrient fluid in the capillary system of plants and 

 animals. 



That the motion of the capillary currents in animals is 

 induced by the vital processes going on in the tissues, and 

 is not to be attributed to the muscular contractions and 

 dilatations of the central organs of circulation, is evident 

 from the following facts : 



* See Draper " On the Forces which produce the Organization of 

 Plants." 



