ii NUTRITION 247 



with living protoplasm that of the prey which is killed 

 and broken up into diffusible proteids, these being after- 

 wards re-combined to form new molecules of the living pro- 

 toplasm of Amoeba. So that the food of Amoeba is, to 

 begin with, as complex as itself, and is first broken down by 

 digestion into simpler compounds, these being afterwards 

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

 the other hand, we start with extremely simple compounds, 

 such as carbon dioxide, water, nitrates, sulphates, &c. 

 Nothing which can be properly called digestion, *.<?., 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 con- 

 taining ready-made proteids, and cannot build up their pro- 

 toplasm 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 holo- 

 phytic 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 



