PHYSIOLOGICAL ACTIVITIES OF THE PROTOZOA 81 



extent from those obtained by Greenwood in the case of carchesium, 

 where the acid reaction is not forthcoming until after the "state of 

 storage," a state varying in length of time from one to twenty hours. 

 The chemical reactions in the later periods were not observed. 



The protozoon, therefore, like phagocytes, evidently has the power 

 of secreting different kinds of ferments in response to the stimulus of 

 different kinds of living food particles. Not only proteolytic, but 

 other kinds of ferments as well are formed in the various types of 

 protozoa, although not by all kinds. Thus, some types of protozoa are 

 able to create starch dissolving ferments similar to the diastatic fer- 

 ments of higher animals, or fat emulsifying ferments similar to steap- 

 sin. In many forms, however, the starch grains, like other indigestible 

 parts, are thrown out of the body untouched (Greenwood, Fabre- 

 Domergue, Meissner). 



The granules that are formed by the breaking down of food par- 

 ticles through the digestive process are ultimately distributed by means 

 of the protoplasm streaming to all parts of the protozoon. Some are 

 probably converted directly into protoplasm by an assimilative pro- 

 cess that is as little understood in these forms as in the metazoa, a 

 process involving synthetic changes whereby the relatively complex 

 food elements are built up into still more complex protoplasmic 

 molecules, thus leading to the repair of waste and to growth. Other 

 granules are not immediately assimilated, but are stored up in the 

 protoplasm as a reserve of nutriment. In these cases it is impossible 

 to say whether such granules are utilized directly as fuel for functional 

 activity through oxidation, or whether they are first built up into pro- 

 toplasm and the protoplasm itself, or its products, oxidized. In all 

 protozoa these reserve matters are present, giving the characteristic 

 granular appearance to the protoplasm of these forms, and their dis- 

 appearance may be easily followed by starving the individual. A 

 paramecium, for example, when normal and active, has a character- 

 istic granular appearance, while numerous gastric vacuoles are dis- 

 tributed throughout the inner protoplasm. When it is starved these 

 granules disappear first of all, and then, with continued starvation, 

 the protoplasmic network is used as a source of energy for the active 

 animal, and great vacuoles appear which increase in size with starva- 

 tion, while the size of the cell decreases to an eighth or a sixteenth 

 of the normal volume, the macronucleus alone, although frequently 

 fragmented, retaining its normal volume. 



It often happens that some one of the many functions of metabolism 

 fails to act, and the organism suffers from the failure to assimilate or 

 from lack of oxidative ferments. I have frequently seen Paramecium 

 aurelia so filled with these reserve food granules that its protoplasm 

 appeared dense and black under the microscope (Fig. 26). In such 

 cases there are no gastric vacuoles, food taking and movement stop, 

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