146 



GENERAL PHYSIOLOGY 



The cilia of the ciliary wreath of the peristome contract continually 

 and rhythmically, and in this way produce in the water a whirlpool, 

 which is so directed that it sucks small particles, such as detritus, 

 mud, bacteria, algae, etc., which are suspended in the water, into 

 the cell-mouth ; from there, surrounded by a layer of water, they 

 are shoved by contractions of the body into the cell-pharynx, and 

 thence into the endoplasm (Fig. 46). The phenomena may be 

 very easily observed, if, according to Ehrenberg's method ('38), 

 granules of carmine or indigo be mixed with the water. It is seen at 

 once how the Vorticclla engulfs the red or blue granules and forms 

 them in its protoplasm into balls which are surrounded by a cover- 

 ing of water and constitute food-vacuoles. 



The mode of ingestion cif food by other Infusoria is entirely similar 

 to that of Vorticella. The free-swimming forms frequently seek fixed 



Fig. 46. — Vorticella in four successive stages of the process of food-ingestion. An alga-cell is 

 being engulfed into the ccU-moath and taken through the pharynx into the endoplasm. 



food-masses and engulf them. Many Infusoria even, such as 

 Ooleps, a small, egg-shaped, ciliate form having a delicate lattice- 

 like surface, take in large balls of food which are broader than their 

 mouth-opening by pressing the latter upon the ball by the force of 

 the ciliary contraction so that the mouth-opening, as in a snake, is 

 gradually enlarged. Thus they really suck the food-balls into 

 their bodies (Fig. 47). 



The ingestion of solid food on the part of the cell is, therefore, 

 in every case brought about by active movements of the cell- 

 protoplasm or its motile organoids. 



In the ingestion of substances by the living ced, one phenomenon 

 deserves special mention — namely, the fact of the selection of food. 

 Of the various cells living in the same medium, each takes to 

 itself different materials, and such as are necessary for the forma- 

 tion of its characteristic substance. This is clear in the tissue- 

 cells of highly organised animals, such as the human body. Here 

 the blood-plasma is the common nutrient material for all tissue- 



