116 PROTOZOOLOGY 



is no indication that they are utilized as food reserves. The ratio of 

 reduced weight and volume and the specific gravity remain reason- 

 ably constant during starvation (Zeuthen, 1948). Andresen (1945) 

 found starved Amoeba proteus to show a similar change on the whole, 

 except that the number of chondriosomes decreased and in some 

 cases dissolution of crystals occurred just before disintegration. 



Respiration 



In order to carry on various vital activities, the Protozoa, like 

 all other organisms, must transform the potential energy stored in 

 highly complex chemical compounds present in the cytoplasm, into 

 various forms of active energy by oxidation. The oxygen involved 

 in this process appears to be brought into contact with the sub- 

 stances in two ways in Protozoa. The great majority of free-living, 

 and certain parasitic forms absorb free molecular oxygen from 

 the surrounding media. The absorption of oxygen appears to be 

 carried on by the permeable body surface, since there is no special 

 organella for this purpose. The polysaprobic Protozoa are known 

 to live in water containing no free oxygen. 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. The parasitic Protozoa of 

 metazoan digestive systems live also in a medium containing no 

 molecular oxygen. All these forms appear to possess capacity of 

 splitting complex oxygen-bearing substances present in the body to 

 produce necessary oxygen. 



Several investigators studied the influence of abundance or lack 

 of oxygen upon different Protozoa. For example, Putter (1905) dem- 

 onstrated that several ciliates reacted differently when subjected to 

 anaerobic condition, some perishing rapidly, others living for a con- 

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

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

 ucts. 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, supposed that the dif- 

 ference in longevity of aerobic Protozoa in anaerobic conditions was 

 correlated with that of the amount of reserve food material such as 

 protein, glycogen and paraglycogen present in the body. Putter fur- 

 ther noticed that Paramecium is less affected by anaerobic condition 

 than Spirostomum in a small amount of water, and maintained that 



