FUNDAMENTAL FACTS 9 



movements which are apparently determined by inter- 

 nal conditions of the living system. Strictly speaking, 

 no movements of animals are exclusively determined 

 by internal conditions, for the atmospheric oxygen 

 and a certain temperature or certain limits of tem- 

 perature are always necessary in order to preserve 

 the activity beyond a short period of time. 



We must discriminate between simple and conscious 

 spontaneity. In simple spontaneity we must consider 

 two kinds of processes, namely, aperiodic spontaneous 

 processes and rhythmically spontaneous or automatic 

 processes. The rhythmical processes are of import- 

 ance for our consideration. Respiration and the 

 heart-beat belong to this category. The respiratory 

 movements prove without possible doubt that auto- 

 matic activity can arise in the ganglion-cells, and 

 from this the conclusion has been drawn that all 

 automatic movements are due to specific structures 

 of the ganglion-cells. Recent investigations, how- 

 ever, have transferred the problem of rhythmical 

 spontaneous contractions from the field of morphology 

 into that of physical chemistry. The peculiar quali- 

 ties of each tissue are partly due to the fact that it 

 contains ions (Na, K, Ca, and others) in definite 

 proportions. By changing these proportions, we can 

 impart to a tissue properties which it does not ord- 

 inarily possess. If in the muscles of the skeleton 

 the Na ions be increased and the Ca ions be reduced, 

 the muscles are able to contract rhythmically, like the 

 heart. It is only the presence of Ca ions in the 



