304 APPLIED BIOLOGY 



Foods. Like every other animal, it requires foods which 

 have been made, directly or indirectly, by plants. These 

 foods are taken in through its mouth and gullet, are digested 

 by enzymes which are believed to be similar to those which 

 cause digestion in higher animals, and the digested foods 

 are absorbed by the protoplasm. Finally, the indigestible 

 substances are ejected from the body. And for all these 

 processes there are no special organs like stomach, intestine, 

 liver, and pancreas in a frog. 



Oxygen. Like every other animal, it requires oxygen. It 

 must breathe; but it has no lungs, as have higher animals. 

 However, its delicate cell-wall allows the absorption of an 

 abundance of oxygen from the surrounding water. Para- 

 mecia soon die in water from which the oxygen has been 

 removed. 



Oxidation and Excretion. Like every other animal, a para- 

 mecium's food is constantly being oxidized to furnish energy 

 to run the living machine ( 42), and this union of oxygen 

 and foods forms excretions. As in a frog, these are chiefly 

 water, carbon dioxide, and nitrogenous excretion. The car- 

 bon dioxide is absorbed by the surrounding water. The water 

 and the nitrogenous excretion is pumped out by the regular 

 pulsations of the contractile vacuoles. Thus, without lungs, 

 kidneys, or skin, a paramecium gets rid of the same excre- 

 tions which in the frog and other higher animals must be 

 eliminated by these organs. 



Assimilation. As in every other animal, some food must 

 be used continually for making new protoplasm, by assimila- 

 tion. Protoplasm is continually wearing out and some food 

 (especially proteins) must be used for making new particles 

 of protoplasm to replace those worn out or destroyed. Also, 

 the animals are frequently dividing, and every new individual 

 is half the usual size and must make enough new protoplasm 

 to double its size before it can reproduce. Hence, much food 

 must be used to make new protoplasm for growth ( 42). 



