I AMOEBA 13 



interior of the drop of chloroform forcing it into a coil. There is again 

 no reason to doubt that the ingestion of the vegetable filament by the 

 Amoeba is brought about by the action of surface tension. 



The Amoeba, as we have seen, feeds and the products of digestion 

 are absorbed and built up into new living protoplasm. Although 

 normally this results in increase of bulk, growth, it does not do so neces- 

 sarily. An Amoeba or other animal may go on absorbing food material 

 and yet show no increase in size. This indicates that in the living body 

 there goes on not merely a process of building up new protoplasm but 

 also a breaking down of the existing protoplasm. While on the one hand 

 relatively simpler substances derived from the food are constantly being 

 built, up into the enormously complex living protoplasm, at the same time 

 the living protoplasm is undergoing a process of breaking down into less 

 complicated non-living substances. The sum total of these processes 

 constitutes what is known technically as metabolism. It is further 

 customary to distinguish the building up processes by the name anabolism 

 and the breaking down processes by the name catabolism. These names 

 are of practical convenience but the student should guard from the 

 commencement against the fallacy that attaching a long technical name 

 to a phenomenon necessarily implies any increase in our knowledge 

 concerning it. As a matter of fact very little is known regarding the 

 intimate nature of metabolic processes. One of their characteristic 

 features is their accompaniment by oxidation. The catabolic processes 

 in fact are as it were accompanied by a slow process of combustion. In 

 many of the larger animals with active metabolism the temperature of 

 the body is actually raised considerably above that of the surroundings 

 by this process of combustion. In a tiny creature like Amoeba this is not 

 perceptible, but, no doubt, could we test its temperature by a sufficiently 

 dehcate and reliable method, we should find that even it is slightly 

 warmed up by its oxidation processes. 



In the living creature at any one particular time there may be com- 

 plete metabolic balance — the anabolic and the catabolic processes simply 

 counteracting one another — or one of them or the other may preponderate. 

 If anabolism preponderates the creature increases in bulk, if catabolism 

 preponderates diminution of the Hving substance takes place. In the 

 latter event there may be no visible shrinkage in bulk, for the diminution 

 of hving substance may be made up for by the accumulation within 

 the body of bulky non-living substance formed by its breaking down. 



An important detail in connexion with the metabolism of Amoeba 

 has to do with the nature of the food. This must ..contain ready-made 

 proteins for the Amoeba is quite unable to build up its protein out of 



