CONVERSION OF PABULUM. 91 



Usually, of the formed material produced, part accumu- 

 lates on the surface of the germinal matter and part escapes. 

 Consider what occurs in the nutrition of ordinary yeast. 

 A layer of cellulose matter which increases by the addition 

 of new layers to its inner surface is formed externally. 

 Within this is the transparent living or germinal matter. 

 When such a particle is nourished, the pabulum passes 

 through the cellulose wall into the germinal matter, and thus 

 the substance increases ; but at the same time some of the 

 germinal matter becomes converted into new cellulose, 

 which is added to that already existing, and alcohol, water, 

 and carbonic acid, which escape. The germinal matter 

 differs from the pabulum, and both differ in physical cha- 

 racters and chemical composition and properties from the 

 cellulose envelope. We cannot make the cellulose or the 

 germinal matter from the pabulum, nor can the pabulum be 

 obtained, as it was before, from either of the above substances. 

 How different are all these processes from the mere addition 

 of matter previously held in solution, as occurs in the 

 formation of a concretion, or a crystal, which increases by 

 the superposition of layer upon layer ! 



Some writers, yielding to the suggestions of fancy and 

 vague speculation, instead of resting upon the firm ground 

 of observation and experiment, have endeavoured, without 

 having at command facts to justify such a conclusion, to 

 make people believe that there are forms very low in the 

 scale of living beings which appropriate inorganic materials 

 only, and which may, therefore, be very similar to the very 

 first living things which appeared upon the earth, and are, 

 in fact, according to this view, their direct descendants, 



