276 G. M. FRANK AND A. D. SNEZHKO 



])rocess, being considerably changed in different ways under the action 

 of pharmacological agents, drugs in particular. 



Now a very difficult question arises : what determines the rhythmical 

 character of the oxygen content. On the one hand, the jjoint can be 

 the rhythmical variation of local blood circulation, the vasomotor 

 periodicity. On the other hand, the rhythm of oxidative processes 

 themselves cannot be ruled out. 



Forestalling the events, it should be pointed out that, having no 

 possibility for the time being of rejecting the first cause, experiments 

 carried out on an entire animal lead us towards the acceptance of the 

 important role played by fluctuation of the rates of oxidative processes. 



This is based on the fact that the rhythmical character of the free 

 oxygen level can be observed in a metabolizing tissue not only when 

 blood circulation is cut off but also in several objects lacking this 

 latter completely. 



(a) 



1 min Imin 



Fig. 5. — Change of rliythm in the rabbit brain as tlie result of head irradiation, (a) cortex ; 



(b) subcortex. 



1, before irradiation; 4, 3 hr after irradiation; 



2, 10 min. later; .5. 6 hr after irradiation; 



3, 1 hr after irradiation; (5, 24 hr after irradiation. 



With a change in free oxygen level in tissue after irradiation and 

 with a change of the curve of "oxygen test", disturbances of this rhythm 

 are also observed. In many instances, 8 to 10 min after termination of 

 exposure the rhythm disappears completely both in the cortex and in 

 the subcortex (Fig. 5). The restoration of this rhythm proceeds in a 

 different fashion. As a rule, the quicker oscillations are restored after 

 30 min, while the depression of the slower ones can be preserved for a 



