INTRODUCTION 145 



which by reason of their generic relationship are included with the 

 protozoa are capable under the action of sunlight of manufacturing 

 starch. Such are said to be holophytic. Other protozoa live upon 

 organic material in solution, the saprozoic mode of life, and finally- 

 some are especially adapted to Uve at the expense of other animals and 

 are parasitic in nature. In the latter instance food may be obtained 

 from the fluids in which they Hve by absorption as is the case with 

 trypanosomes living in blood plasma or cells may be ingested as in the 

 ca,se of dysentery amoebae. 



" The process of respiration in the protozoa is in general similar to 

 that of higher animals. Most of them require oxygen and eliminate 

 carbon dioxide. The contractile vacuole which is found in certain- 

 forms is believed to have a respiratory function. Respiration may 

 consist of the liberation of energy through oxidation or through the 

 breaking down of complex molecules. In organisms of an anaerobic 

 habit the respiration is probably through internal molecular changes 

 affecting material stored in the cytoplasm. 



" In addition to the expulsion of solid undigested material from 

 the cytoplasm there is evidence that waste products other than COj 

 are excreted by contractile vacuoles. Many organisms also secftete 

 material either of the nature of chitinous membranes on their surface 

 or metabolic products in the form of globules, etc., within their bodies. 



" The most obvious evidence of liberation of energy in the physiology 

 of protozoa is seen in their movement. Certain protozoa, Nocticula 

 for example, however, emit light and produce the phosphorescence 

 often observed in sea water. From analogy with higher animals it is 

 to be supposed that heat and electrical changes are also produced. 



" Certain chemical substances which attract protozoa are said to be 

 positively chemotactic, others which repel negatively chemotactic. Vari- 

 ous forms react in a definite manner to light— phototaxis, heat— 

 thermotoxis, gravity — geotaxis, etc. 



" Derangement of function may be produced associated with which 

 are visible degenerative changes. It has also been found that certain 

 protozoa have the abiUty to recover from injury and to regenerate lost 



parts." 



Energy Supply op Microorganisms. — ^The source of energy in 

 microbial life is always of chemical origin. The simplest processes 

 are the oxidations, and simplest among these the inorganic oxidations. 



10 



