194 THE PROTOZOA 



Some doubt has existed as to the power possessed by Protozoa 

 of digesting fats, and, according to Staniewicz (208), no digestion 

 of fat takes place in Infusoria. According to the recent investiga- 

 tions of Mrenstein (182), however, Paramecia under natural con- 

 ditions contain fat in more or less considerable quantities. By 

 choice of suitable food, the quantity of fat in the endoplasm can be 

 increased greatly. The fat-granules serve as reserve-nutriment, 

 and disappear under starvation. Paramecia which have lost their 

 fat in this way, if then d with milk, oil-emulsion or yolk of egg 

 rubbed up in water, show in a few hours the endoplasm full of fat- 

 granules ; if fed with starch or particles of egg-albumen, the same 

 result is obtained, but not to anything like the same extent. 

 Experiments on fatty substances ingested by the animals showed 

 that the fat remains unaltered during the first (acid) period of the 

 digestion in the food-vacuole, and is digested during the second 

 (alkaline) period. Feeding with fatty acid and glycerine also leads 

 to storage of fat in the endoplasm. If fed with oil-globules stained 

 with Soudan III., unstained oil-globules appear in the endoplasm. 

 Nirenstein concludes from his observations that the fat is broken 

 up into its soluble components in the vacuole, and synthesized again 

 to neutral fat in the endoplasm. 



The indigestible residues of the food are ejected from the body 

 either at any point on the surface, in amoeboid forms, or through a 

 definite aperture, in corticate forms. A great accumulation of 

 faecal matter may take place in some cases, as in the " stercome " 

 of Foraminifera (p. 233), of which the animal purges itself 

 periodically. 



(c) Saprophytic and Parasitic Nutrition. In this type the 

 organism absorbs its nourishment by diffusion through the surface 

 of the body without the aid of any visible organs or structural 

 differentiations of any kind. Practically nothing is known of the 

 mechanism by which this is effected or of the chemical processes 

 involved, but it is probable that enzymes secreted by the organism 

 reduce the nutritive particles to a soluble form prior to absorption. 

 There is reason to believe that the nucleus is specially concerned 

 in the production of enzymes, and in many species, parasitic or 

 otherwise, the behaviour of the nucleus indicates a relationship 

 between it and the process of absorption of food-substance. In 

 Carchesium, as already stated, the path along which the food- 

 vacuoles travel runs close along the inner edge of the horseshoe-shaped 

 macronucleus (Greenwood, 162) ; in Euplotes, similarly, the large 

 macronucleus encloses an area containing all the food-vacuoles 

 (Fig. 182). According to Wallengren (214), the reactions of the 

 food-vacuoles of Paramecium change as they pass the nucleus, and 

 the function of the cyclosis in the endoplasm is to bring the food- 



