494 GENERAL PHYSIOLOGY 



that correspond to the excited components of biotonus. But it is 

 questionable whether this case is actually realised in nature. 



Among the various cases of interference between two stimuli 

 there is a very great variety of phenomena which have not yet 

 been analysed at all, but which ought to receive new light from 

 the foregoing reflections. One group, particularly, which pertain 

 to the functions of the central nervous system, and thus far have 

 been among the most obscure phenomena of nerve-physiology, will 

 be elucidated ; these are the so-called phenomena of " inhibition " 

 [ffemmunffl. 



Heretofore there have been considerable difficulties in the way 

 of a physiological explanation of the simple fact of the voluntary 

 interruption of a movement, for example, the simple letting-down 

 of a raised arm. The lack of clearness in the problems of inhibi- 

 tion depends chiefly upon insufficient sharpness in distinguishing 

 the conceptions. Inhibition [Hemmtmg] and depression [Lcihmung] 

 have often been confused with each other upon the ground of 

 purely external features ; yet, as has been seen, an inhibitory 

 reaction in the cell is not necessarily due to depression, but may 

 be caused by the excitation of processes that oppose existing ones. 

 The stopping or retarding of a muscular movement by a motor 

 ganglion-cell can be the expression of two very different processes. 

 According to the general view, as is well known, the contraction 

 of a muscle is caused by an excitation of dissimilation in its motor 

 ganglion-cells. An expansion can, therefore, originate in the 

 ganglion-cell in two ways : first, by a depression of dissimilation, 

 and, second, by an excitation of assimilation. As regards the 

 muscle, the two have the same result. Hence it is necessary 

 to decide in any one case what processes are taking place 

 in the participating ganglion-cells. Among the manifold pheno- 

 mena of the inhibition of motion doubtless both cases are present. 

 The frog whose hinder extremities will not perform reflex move- 

 ments with the strongest stimuli for some time after the upper 

 part of its spinal cord is severed, has evidently experienced a 

 temporary depression of the ganglion-cells of its cord through 

 over-stimulation, just as in surgical shock as a result of a severe 

 operation the nervous system is depressed. But the voluntary 

 relaxation of a contracted muscle can hardl)^ be due to tiuch 

 depression. In this case there must be an inhibition of con- 

 traction caused by the excitation of antagonistic, i.e., expansory 

 processes. 



The fact that the expression of an excitation can be stopped by 

 the excitation of antagonistic metabolic processes appears to play 

 a very important rSk in the life of ganglion-cells, and to afford a 

 very important factor in the explanation of many processes in the 

 central nervous system. 



Especially the phenomena of sleep and hypnosis in animals and 



