ii NUTRITION 247 



diffusible proteids, these being afterwards re-com Dined 

 to form new molecules of the living protoplasm of 

 Amoeba. So that the food of Amoeba is, to begin with, 

 as complex as itself, and is first broken down by diges- 

 tion into simpler compounds, these being afterwards 

 re-combined into more complex ones. In Sphaerella, on 

 the other hand, we start with extremely simple com- 

 pounds, such as carbon dioxide, water, nitrates, sul- 

 phates, &c. Nothing which can be properly called 

 digestion, i.e., a breaking up and dissolving of the food, 

 takes place, but its various constituents are combined 

 into substances of gradually increasing complexity, 

 protoplasm, as before, being the final result. 



To express the matter in another way : Amoeba can 

 only make protoplasm out of proteids already formed 

 by some other organism : Sphaerella can form it out of 

 simple liquid and gaseous inorganic materials. 



Speaking generally, it may be said that these two 

 methods of nutrition are respectively characteristic of 

 the two great groups of living things. Animals require 

 solid food containing ready-made proteids, and cannot 

 build up their protoplasm out of simpler compounds. 

 Green plants, i.e., all the ordinary trees, shrubs, weeds, 

 &c., take only liquid and gaseous food, and build up 

 their protoplasm out of carbon dioxide, water, and 

 ' mineral salts. The first of these methods of nutrition is 

 conveniently distinguished as holozoic, or wholly-animal, 

 the second as holophytic, or wholly- vegetal. 



It is important to note that only those plants or parts 

 of plants in which chlorophyll is present are capable of 

 holophytic nutrition. Whatever may be the precise 

 way in which the process is effected, it is certain that 

 the decomposition of carbon dioxide which characterises 

 this form of nutrition is a function of chlorophyll, or, to 

 speak more accurately, of chromatophores, since there 



