THE PROCESSES OF DEPRESSION 239 



restriction of the perceptible response to stimulation. In the 

 same degree in which oxydative disintegration becomes less, 

 awoxydative breaking down products are accumulated. The 

 accumulation of these products likewise plays a part in the pro- 

 duction of depression and increases the decrement in the con- 

 duction of excitation. The decrease of energy production by 

 decline of the oxydative decomposition, as well as the accumu- 

 lation of anoxydative breaking down products, therefore, simi- 

 larly reduce irritability; that is, their effect is depressing. This 

 whole series of processes, which we have previously considered 

 in detail, takes place on the withdrawal of oxygen and leads to 

 the depression of asphyxiation. It can readily be observed in 

 the most varied kinds of aerobic organisms in rhizopods and 

 infusoria, in plant and ganglion cells, but finds its most complete 

 demonstration in the nerves. Here these processes can be easily 

 produced with any rapidity desired, accordingly as a relative or 

 absolute want of oxygen is brought about. These same typical 

 results are likewise shown in numerous processes in which the 

 external conditions are quite different in nature. 



We have previously become acquainted with such a case and 

 studied it in detail. This is the state of fatigue. Fatigue is a 

 typical state of depression, that is, a state in which the vital pro- 

 cess is retarded and irritability in response to stimuli corre- 

 spondingly decreased. Fatigue is, however, as we have found, 

 the result of a relative deficiency of oxygen. The amount of 

 oxygen at disposal is not sufficient to allow of disintegration, 

 increased by constant functional activity oxydatively taking place, 

 to develop to its full extent. In consequence the previously cited 

 sequence of processes takes place. A "depression of activity" is 

 produced. Fatigue is true asphyxiation and it is here evident 

 that depression proceeds from the same constituent processes of 

 metabolism as excitation, brought about by a single stimulus. 

 Excitation produced by constant stimuli gradually merges into 

 depression as the amount of oxygen at disposal, even if augmented 

 in the intact organism by the increased blood supply, for instance, 

 is still insufficient to meet the demand made by the increased 

 oxygen consumption as a result of continuous functional activity. 



