PHYSIOLOGY 97 



For example, Noland (1927) observed Metopus es in a pool, 6 feet 

 in diameter and 18 inches deep, filled with dead leaves which gave 

 a strong odor of hydrogen sulphide. The water in it showed pH 7.2 

 at 14°C., and contained no dissolved oxygen, 14.9 c.c. per liter of 

 free carbon dioxide, and 78.7 c.c. per liter of fixed carbon dioxide. 

 It is considered that endozoic Protozoa of metazoan digestive 

 systems live also in a medium containing no dissolved oxygen. All 

 these forms appear to possess capacity of splitting complex oxy- 

 gen-bearing substances present in the body to produce necessary 

 oxygen. The liberation of energy is accompanied by production of 

 water and carbon dioxide. 



Several investigators studied the influence of abundance or 

 lack of oxygen upon different Protozoa. For example. Putter dem- 

 onstrated that several ciliates reacted differently when subjected 

 to anaerobic condition, some perishing rapidly, others living for a 

 considerable length of time. Death is said by Lohner to be brought 

 about by a volume-increase due to accumulation of the waste 

 products. When first starved for a few days and then placed in 

 anaerobic environment, Paramecium and Colpidium died much 

 more rapidly than unstarved individuals. Putter, therefore, sup- 

 posed that the difference in longevity of aerobic Protozoa in ana- 

 erobic conditions was correlated with that of the amount of reserve 

 food material such as protein, glycogen and paraglycogen present 

 in the body. Noting Paramecium is less affected by anaerobic con- 

 ditions than Spirostomum in a small amount of water, Putter 

 maintained that the smaller the size of Protozoa and the more 

 elaborate the contractile vacuole system, they suffer the less lack 

 of oxygen in the water, since the removal of catabolic waste de- 

 pends upon these factors. 



The variety of habitats and results of artificial cultivations of 

 various Protozoa clearly indicate that the oxygen requirements 

 vary a great deal among different forms. Attempts were made in 

 recent years to determine the oxygen requirement of Protozoa. 

 The results of the observations are not always convincing. The 

 oxygen consumption of Paramecium is said, according to Lund 

 (1918) and Amberson (1928), to be fairly constant over a wide 

 range of oxygen concentration. Specht (1934) considers the meas- 

 urements of the oxygen consumption and carbon dioxide produc- 

 tion in Spirostomum amhiguum vary because of the presence of a 

 base produced by the organism. Soule (1925) observed in the cul- 



