200 



If this table is compared with the foregoing one, the 

 curvatures which hâve occured must be attributed to the 

 oxygen, which after 65 minutes began to replace the 

 nitrogen. Thèse experiments are therefore another proof 

 that perception of the stimulus has taken place, but that 

 without oxygen it cannot express itself in a reaction. 



That the curvatures remain fairly weak in this case (they 

 never became stronger even with a longer observation 

 time), is due to the fact that the stimulus is already 

 falling ofF. From this it directly follows that we cannot 

 speak of the lengthening of the reaction-time in conséquence 

 of deprivation of oxygen, because in that case the maximal 

 reaction after stimulation with 900 m.g.-secs. i.e. a cur- 

 vature of 2 m. m., would hâve to occur later than under 

 normal conditions. 



Of ail this there is no question at ail. What we see is 

 that the reaction cannot occur at ail without oxygen, 

 whilst when the nitrogen is replaced by oxygen at a stage 

 when the stimulus is not yet whoUy exhausted, the reaction 

 can still occur to a slighter degree. An experiment com- 

 pletely in agreement with this explanation is one in which 

 there was a departure from the experiments described 

 above in so far as that I admitted the oxygen 45 minutes 

 after the beginning of stimulation. 

 TABLE 22. 

 Strength of stimulus 900 m.g.-secs. Température 20° C. 



