328 EFFECT OF CHEMICAL AGENTS [Cn. XI 



believed to have little importance as plastic foods --we have 

 chiefly to consider the use of the complex fats, albuminoids, and 

 other organic compounds. We can make little use of the 

 extensive tables of calorific properties of foods which, however 

 important for determining capacity for supplying energy, 

 afford little insight into the plastic properties of the food- 

 its importance for the growth of dry substance or the imbi- 

 bition of water. 



The difficulties in the way of feeding animals upon known 

 nutritive solutions are great, both because solutions are not 

 their normal food, and because, in the case of water organisms, 

 the bacteria introduced with the animals thrive better than 

 they. Consequently the observations on nutritive compounds 

 for animals are meagre. It will be best to consider them 

 under the types upon which they have been made. 



Amoeba. - -We owe important studies on the foods of Amoeba 

 to the fact that some species have a pathogenic importance. 

 Cultures of them have therefore been made by bacterio- 

 logical methods. It is found that various, even innocuous 

 kinds, will grow upon egg albumen in distilled or phenylated 

 water kept at about 15 C. (CftiVELLi et MAGGI, '70, '71 ; 

 MONTI, '95), upon agar-agar sheets from which the soluble 

 substances have been removed by repeated washing in distilled 

 water (BEYERINCK, '96), upon " Fucus [Chondrus?] crispus" 

 (CELLI, '96), or upon slices of potato (GoniNi, '96). It is 

 thus clear that, in addition to salts, Amoeba needs only a very 

 simple nitrogenous diet. It is, however, uncertain whether 

 the amceba feeds directly from the organic food stuff, or indi- 



rectly upon the bacteria which grow 

 upon the food supplied. 



Infusoria.-- A. beginning has been 

 made in the study of this group by 

 FIG. 90. Poiytoma nveila, OGATA ('93), who reared pure cultures 



a flagellate infusorian. Q f ^ flagellate Poiytoma UVella (Fig. 

 (From VERWORN, 95.) rt J . \. e 



90) on plates 01 nutrient gelatine 



(which is extremely rich in protein) and also upon a medium 

 composed of 500 ccm. meat bouillon, 12.5 grammes grape 

 sugar, and 250 grammes of a Japanese mixture of algte called 

 " riori," derived mostly from the species Porphyra vulgaris. 



