VOLUNTARY AND AUTOMATIC MOVEMENTS. 271 



whether there is actually a purely voluntary excite- 

 ment, that is, that no incitement acted externally 

 on the brain but that the excitement originated quite 

 spontaneously, we will not enter further here. All 

 that is certain is that in many cases an action appears 

 to be voluntary which, if the process is more closely 

 analysed, is found to result from external influences. 

 But the physiological process by which (whether 

 externally influenced or not) excitement arises in 

 the nerve-cells, which excitement is then transmitted 

 through the nerve-fibre to the muscle, is as yet ex- 

 tremely obscure ; and if it is said that it is a molecular 

 motion of the constituent particles of the nerve-cell, 

 this explains nothing, but merely expresses the convic- 

 tion that it is not a supernatural phenomenon, but 

 merely a physical process analogous to the process of 

 excitement in the peripheric nerves. ^ 



Involuntary movements occur sometimes irregularly, 

 as twit chin gs, spasms ; sometimes regularly, as in the 

 case of respiratory movements, the movements of the 

 heart, the contractions of the vascular muscles, of the 

 intestinal muscles, and so on. The latter, which occur 

 with more or less regularity while life lasts, and are 

 for the most part of deep significance as regards the 

 normal condition of the vital phenomena, have natu- 

 rally been especially subjected to thorough research. 

 They are called automatic movements, that is, they 

 occur independently of the co-operation of the will, 

 and apparently without any incentive. But notwith- 

 standing this, it is chiefly in such cases that the causes 

 which effect the excitement of the nerves concerned 

 have been to a certain extent established. 



Automatic movements may be distinguished into 



