226 EXPERIMENTAL INVESTIGATION OF THE ACTION OF MEDICINES. 



the oxygen to keep up combustion and evolve energy, and the 

 nourishment necessary to replace the material thus used up, but 

 can at the same time remove the products of waste. In liigher 



Fi&. 124.— Amoeba Princeps. 



An amoeba figured at two different periods during movement. 

 n, nucleus; /, ingested bacillus. 



organisms, the little masses of living material of which they are 

 composed, and which are for the most part fixed, are nourished 

 by a fluid in which they are bathed, fresh portions of it being 

 supplied by its constantly flowing over them, instead of their 

 moving like the amoeba through it. In sponges, for example, 

 where amoeba-like bodies are attached 'to a framework, as 

 shown in the diagram (Fig. 125), a current of water is kept flow- 



Fia. 125. — Hypothetical Section of SpoDgilla. 



[After Huxley.] It consists of a number of particles, each resembling an 

 ■amoeba, and supported by a fibrous framework. It is divided into a super- 

 ficial layer (a) and a deeper part (e), separated by a cavity. The particles of 

 which e is composed would not get enough nourishment were it not that a 

 constant current of water is kept flowing over them by the action of the cilia 

 with which some of them (c) are provided. These move constantly in one 

 direction, and thus draw the water in at b and cause it to flow out again at d 

 in the direction of the arrows. 



