PROTOZOA 31 



Protozoa. The chemical composition is probably like that 

 of bacteria, although little is known of it. Their vital activi- 

 ties are influenced by physical conditions, as is the case 

 with all animate beings. They require moisture for their 

 full development, but may live for indefinite times when it 

 is at a minimum. A definite temperature is demanded by 

 each species or genus for its full activity. They are suscep- 

 tible to high degrees and remain quiescent in nature in the 

 cold for a long time. Desiccation of the germinating forms 

 is usually fatal, but when in sporulation or encystment, 

 drying is more easily withstood. Light is not absolutely 

 essential for the growth of protozoa, but they are usually 

 attracted or repelled by it; that is, few if any are indifferent 

 to luminosity. 



