RESPIRATORY METABOLISM 361 



tion, we are able, by means of measurements of O, consumption, to 

 determine directly the amount of energy available to the organism. If 

 oxidation is incomplete, a further knowledge of the oxidation products 

 is necessary. It is usually assumed, unless we have knowledge to the 

 contrary, that oxidation is complete in the aerobic Metazoa (cf. intes- 

 tinal nematodes, von Brand and Jahn, 1940). Among the bacteria and 

 also among the Protozoa this is not always true, even in the presence of 

 normal O, tension. However, since carbohydrate cleavage and intra- 

 molecular oxidation, even in the presence of O2, may be considered an 

 anaerobic process, that question will be discussed under anaerobiosis. 



From studies on the heat of combustion, we know that complete 

 oxidation of glucose yields 677,000 calories per gram molecule, or about 

 3,700 calories per gram. Complete combustion of protein yields 5,700 

 calories per gram, and fats yield 8,000-9,000 calories per gram. There- 

 fore, if we know the substrate being oxidized and the rate at which O, 

 is consumed, we can calculate the energy made available by oxidation. 

 According to the equation 



QHi^O, + 6 O2 -^ 6 CO. + 6 H2O + 677,000 cal. 



one gram molecule of glucose requires six gram molecules of O^. The 

 volume of O, consumed (at N.T.P.) is 6 X 22.4 liters, or 134.4 liters. 

 The ratio of O, consumed to calories released is 134 liters/677,000 

 calories, or about one calorie for each 200 mm'' of O, consumed. Similar 

 calculations may be made for fats and proteins. 



Table 4 contains most of the known data for respiratory rates for 

 the Protozoa which can be expressed in absolute terms — either as mm^ 

 O2 per organism per hour, or mm'^ O2 per gram dry or wet weight per 

 hour. Similar tables are given by von Brand (1935) and Hall (1938). 



2. THE EFFECT OF O, TENSION ON O^ CONSUMPTION 



For many types of biological material it has been quite well established 

 that, under usual experimental conditions, O, consumption is inde- 

 pendent of O2 tension, within very wide limits (exceptions cited by 

 Tang, 1933, McCoy, 1935). Recently, however, Kempner (1936, 1937) 

 demonstrated that this is not true for several species of bacteria, for 

 human leucemic leucocytes, for red blood cells of man, fowl, and alli- 

 gator, and for pine needles if CO2 is present or if the temperature is 



