PHYSIOLOGICAL PROPERTIES OF AMCEBA 165 



that the metabolic phenomena of Amoeba are, broadly speaking, 

 similar to those of higher animals. The katabolic changes are in 

 the long run processes of oxidation, and although their products 

 have not yet been definitely ascertained in Amoeba, there can be 

 no doubt that they consist mainly of carbon dioxide, water, and 

 some form of nitrogenous matter (urea or a related substance). 

 Most of these waste matters are believed to be passed out (se- 

 cretion, excretion) by means of the contractile vacuole, but prob- 

 ably carbon dioxide leaves the body by diffusion through the 

 general surface (respiration in part). 



The materials for the constructive process (anabolism) are 

 derived from organic food-matters bodies or fragments of plants 

 and animals taken as food in the process of alimentation, and 

 absorption from the water and the inorganic salts dissolved in 

 it, and from the free oxygen that enters by diffusion through 

 the general surface (respiration in part). Proteid matter is an 

 indispensable constituent of the food, and Amoeba is therefore 

 an animal. 



Alimentation, absorption, secretion, digestion, and circula- 

 tion, all of which are only the prelude to metabolism, but which 

 in the higher animals are assigned to different organs, tissues, 



O O O 



and cells, are here performed by one and the same cell. The 

 capture of solid food here requires its entrance into the cell ; 

 and the fact that proteids cannot be absorbed by diffusion neces- 

 sitates intracellular digestion which in turn necessitates cellular 

 defsecation. It will be observed that while there is no localized 

 or permanent mouth or anus, the whole surface of the cell is 

 potentially mouth or anus. In short, the protoplasm here ex- 

 hibits not the physiological division of labor, but its absence. 



(4) Growth and Reproduction. Logically there is in the 

 case of Amoeba no good ground for a distinction between these 

 processes and metabolism ; for reproduction is directly or indi- 

 rectly an effect of growth, and growth is simply an excess of 

 anabolism over katabolism. Practically, however, the distinc- 

 tion is necessary ; for the tendency of living things to run in 

 cycles of growth and reproduction is one of their most obvious 

 and characteristic features. 



Here, as in all protoplasmic structures, growth takes place 

 throughout the mass, by intussusception (p. 4), not by the ad- 



