THE RHYTHM OF OXIDATIVE PROCESSES 2 



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As is well known, tliis procedure was applied for the first time by 

 Davies and Brink (11)42) for the direct measurement of the free oxygen 

 tension in the tissues of a living animal. These workers develo])ed various 

 kinds of electrodes. VV^e used the sim])lest modification consisting of the 

 insertion of an open platinum needle. Without making it possible to 

 determine the absolute oxygen content, this modihcation allowed us 

 to demonstrate and to follow simply the relative changes in free 

 oxygen content in tissues at the expense of the component determined 

 by diffusion current which, in its turn, was determined by the concen- 

 tration of free oxygen. These papers are published (Snezhko, 1956, 

 1957) and I shall not dwell on them any longer. 



It was just this open platinum electrode which allowed us to realize 

 the procedure of long term continuous recording of relative changes in 

 free oxygen content. At the same time an accessory procedure, called 

 "oxygen test" turned out to be a specified test and simultaneously the 

 check of the behaviour of oxygen itself in tissues. For this experi- 

 mental animals are exposed to a short inhalation of pure oxygen in 

 strictly controlled doses. This leads to a short term enrichment of 

 tissues in oxygen which is well registered polarographically. The level 

 of this enrichment, as well as "resolving" the curve of the excessive 

 oxygen concentration after the cessation of inhalation was found to be 

 specific and served as a quantitative index not only of haemodynamic 

 conditions but of the rate of oxygen utilization by the tissue as well. 



In other words, with an increase of oxygen concentration in the air 

 inhaled by the animal, the current (which is directly correlated with the 

 concentration of tissue oxygen) increases for the time of inhalation. 

 After the influx of this air ceases the current diminishes to the initial 

 value. An increase takes place some 2 to 5 sec. after the start of the 

 oxygen flow. Some seconds after the cessation of this flow the current 

 still continues to increase. The current registered falls to its initial value 

 1-5 to 2 minutes after the arrest of the flow. 



The advantage of this method is that the value for the accessory 

 current designed as At in pure form is determined by the excessive 

 oxygen concentration in the tissue, while, when applying the open 

 electrode, the main current is partially related to side-phenomena. 



Apart from this, the utilization curve of the excess amount of oxygen 

 is, as was mentioned above, a good index of the functional state of the 

 tissue. 



In the experiments on rabbits, the behaviour of free oxygen in the 

 tissues of the central nervous system was the first to be studied. For 

 this several electrodes were inserted in different parts of the system. In 

 our opinion, this was the start of the topographical study of processes 



