THE RHYTHM OF OXIDATIVE PROCESSES 273 



As to sections and tissue homogenates, as well as to simpler objects, 

 such as sea urchin eggs and plants, here an inhibition of tissue respira- 

 tion is observed as a rule. From this view])oint the data obtained in 

 our laboratory are in agreement with the observations on tissue respira- 

 tion in vitro. The advantage consists, however, in that, as we shall see 

 below, this method allows the possibility of following up tissue response 

 in vivo and of sufficiently distinctly determining the curve of this re- 

 sponse against time. 



Most distinct results are obtained with the aid of the "oxygen test." 

 The curve of an increase in diffusion current in response to the in- 

 halation of a dose of oxygen is determined several times for each 

 experimental animal. This curve is, as a rule, quite typical and stable 

 in its shape and amplitude for each given animal and for a definite 

 position of the electrodes. 



After total iiTadiation with a dose of the order of 1,000 r, or after local 

 irradiation to the head with doses from 1,000 to 3,000 r, the diffusion 

 cvirrent starts to increase some 5 to 10 minutes after irradiation. The 

 maximum of this increase, A/, is reached two to three hours after 

 exposure. The curve rises and the time at which it begins to fall, i.e. 

 the time of utilization, increases conspicuously, up to twofold and more. 

 The time of utilization is often disproportionately prolonged, much 

 more than the amplitude increase. 



Taking into consideration that this peculiar change of the reaction 

 proceeds against the background of progressive haemodynamic dis- 

 turbances, it can be ascribed only to a deterioration of the ability of the 

 tissue to utilise oxygen. 



Of key significance is the fact that this reaction is by no means a 

 result of complex secondary or tertiary changes, and bears witness to 

 the direct local response of the tissue. In more general form this was 

 demonstrated by us upon a change in the localization of the action. 



Shielding of the head and irradiation of the abdomen leads to reverse 

 pictures in the behaviour of the "oxygen test'' which point to de- 

 ficiency of free oxygen at the root of haemodynamic disturbances. 

 Compared with the control, prior to irradiation, oxygen dosage causes 

 no increase; moreover, it brings about a clear decrease (Fig. 2). 

 The additional amount of oxygen is greedily utilized by the tissues of 

 the irradiated organism. 



Indeed, no concept of activation of oxidative processes arising in the 

 central nervous system following abdomen irradiation is required here. 

 It suffices to perceive clearly that a tissue is able to cover a deficiency 

 associated with a disturbance of blood circulation at the expense of an 

 additional portion of oxygen. 



