102 NUTRITION. 



operations by which changes are effected in substances by 

 living matter, are in their nature essentially different from 

 those which man is obliged to employ to bring about changes 

 of a similar kind out of the body ; and until we are taught 

 what the agent or operator in the living matter really is, it is 

 surely permissible to call it vital power. Its actions cannot 

 be denied and ought not to be ignored. 



It seems to me childish, rather than philosophical, on the 

 part of any one to reassert in these days that nutrition is 

 merely a chemical process, unless he can imitate by 

 chemical means the essential phenomena which take place 

 when any living thing is nourished. The passage of a fluid 

 through a tissue by which its structure is preserved is not 

 nutrition, or the introduction of preservative fluids into dead 

 tissues would be a nutritive operation. A fluid may hold in 

 solution certain substances which are separated from it as it 

 traverses the tissue, thus adding weight and altering the 

 properties of the tissue, as occurs when calcareous and other 

 slightly soluble substances are deposited in the soft matrix of 

 bone, teeth, shell, and other textures. This is a process which 

 can be made to take place in lifeless matter, and has been 

 adduced in support of the doctrine that the tissues of plants 

 and animals are formed by physical and chemical agencies 

 only ; but it is not nutrition. Those who advance such 

 arguments confuse the process of deposition of insoluble 

 salts in a material previously formed, with the actual forma- 

 tion of the material itself out of substances of a totally 

 different composition. 



Nutrition, then, involves the conversion of lifeless pabu- 

 lum into living germinal matter, and comprises these steps. 



