174 IRRITABILITY 



cesses depend essentially upon the question, if the oxydative dis- 

 integration itself in the given living system occurs in one single 

 phase, in that the oxygen is the activator for the oxydative split- 

 ting up of the carbon chain, or if this takes place in two periods, 

 in which the carbon chain is first anoxydatively split up into 

 larger fragments by the stimulus, which are then seized upon by 

 the oxygen to be split up into carbon dioxide and water. As we 

 have seen, this question must remain for the present undecided 

 as far as the metabolism of rest as well as the excitation pro- 

 duced by a single momentary stimulus is concerned. It is highly 

 probable that a uniformity of the process for all living systems 

 does not exist. We are, therefore, not justified in assuming that 

 these special chemical processes resulting from single stimuli are 

 uniform throughout the refractory period. 



On the contrary it is different in the case of oxygen deficiency. 

 Here we see with increasing want of oxygen a constantly increas- 

 ing duration of the refractory period, a prolongation which may 

 be attributed to the retardation of the oxydative disintegration. 

 It is necessary, however, that we now study more clearly these 

 alterations brought about by the deficiency of oxygen. 



If we follow the course of the changes from that of the normal 

 state of equilibrium of metabolism, wherein oxygen is sufficient 

 to bring about complete disintegration of the molecules to the 

 formation of carbon dioxide and water, we must assume in spite 

 of the great explosive rapidity of this process on the basis of our 

 chemical knowledge, that first a series of intermediate products 

 are produced before finally the end products are formed. In 

 this way the oxydative disintegration produced by a stimulus 

 becomes more and more prolonged by an increasing want of 

 oxygen. If, as I have previously suggested, the amount of energy 

 which is liberated in a given space and time by an excitating stimu- 

 lus is taken as a standard of irritability, it is apparent that the 

 more the oxydative disintegration following a stimulus is retarded, 

 the greater must be the decrease in irritability. The less oxygen 

 there is at disposal and the more incomplete the oxydative break- 

 ing down, the smaller is the degree of irritability, the weaker the 

 response and the slower the return of irritability after every 



