Oxidation Systems of Organisms 563 



first instance this refers to the temperattire and the concentration of oxygen in 

 the internal gaseous medium. In plants these factors are characteristically variable 

 with sharp fluctuations, their temperature varies within practically the same 

 limits as that of the surrounding atmosphere. 



The content of O2 and CO2 in the internal gaseous medium of plant tissues 

 is also extremely inconstant. For example, during the course of 24 hours the 

 percentage of O2 in the internal atmosphere of the blades of leaves varies, ac- 

 cording to our findings, from yi to 17-4, while that of CO2 varies from 0-9 to 

 5-1. In organs having a parenchyma of many layers the content of oxygen, 

 depending on the depth of the tissue at which it was measured, varies from 0-8 

 to 17-2% and that of CO2 from 3-0 to 40%. 



The exact opposite is true for warm-blooded animals in which there is, 

 characteristically, not only a constant body temperature, but also a fairly good 

 equalization of the gaseous composition of the tissues. According to Campbell 

 the pressures of O2 and CO2 (in mm Hg) are [i] : 



The situation is different in animals at a lower stage of evolutionary develop- 

 ment. For example, in fish the body temperature fluctuates within the same 

 limits as that of the waters in which they live, exceeding this temperature by only 

 o-3-i-o° C [2]. In cold-blooded animals fluctuations in temperature are also 

 associated with changes in the composition of the gaseous medium. In the toad, 

 for example, also according to Campbell, the oxygen pressure in the subcutaneous 

 tissues at 3° C is 100 mm Hg while at 17° C it is 49 mm Hg. At the same time 

 the pressure of CO2 changes from 4 to 12 mm Hg [2]. It is obvious that the 

 ability to carry out respiration in the face of such sharp variations in temperature 

 and oxygen concentration must be determined, in different groups of animals, 

 by specific peculiarities of the oxidative enzymic systems. 



A consideration of these peculiarities forms the subject of this communication. 



One of the most characteristic metabolic peculiarities, peculiar to green plants, 

 is rhythmicity, which is brought about by regular changes in the action of 

 enzymes. This refers to the seasonal and diurnal rhythms studied in detail in 

 the works of B. A. Rubin, N. M. Sisakyan and others. This rhythmicity affects 

 the most various aspeas of metabolism, among them oxidative metabolism [3]. 



There is now no doubt that the terminal stage of respiration in higher plants 

 can be brought about by the participation of the different oxidases which are 

 normally all present in the tissues of any particular organism at once. 



Apart from the Fe- and Cu- protein enzymes, one must also include in this 

 group tlie flavine enzymes which, until recently, were regarded as enzymes 

 which had no metals in them and which, therefore, were not susceptible to 

 enzymic poisons (KCN, NaNg). 



