56 PROTOPLASM. 



and probably acts like a filter, permitting some things to 

 pass and interfering with the passage of others. In nutrition, 

 pabulum becomes germinal matter to compensate for the 

 germinal matter which has been converted into formed 

 material. Now let us consider the order of these changes, 

 and endeavour to express them in the simplest possible 

 manner. 



Let the germinal matter which came from pre-existing 

 germinal matter be called a; the non-living pabulum, some 

 of the elements of which are about to be converted into 

 germinal matter, shall be b; and the non-living formed 

 material resulting from changes in the germinal matter, c. 



It is to be remarked that b does not contain c in solu- 

 tion, neither can c be made out b unless b first passes 

 through the condition a, and a cannot be formed artificially, 

 but must come from pre-existing a. 



In all cases b is transformed by a into a, and a under- 

 goes conversion into c. Can anything be more unlike 

 chemical and physical change ? Neither a, nor b, nor c can 

 be made by the chemist ; nor if you give him b can he 

 make a or c out of it ; nor can he tell you anything about 

 the "molecular condition" or chemical constitution of a, 

 for the instant he commences his analysis a has ceased to 

 be a, and he is merely dealing with products resulting from 

 the death of a, not with the actual living a itself. The 

 course which the pabulum takes in the nutrition of the 

 germinal matter of a cell is represented by the arrows in 

 fig. 23, pi. VII. 



