x THE FOKE-BBAIN 565 



active state into which it is thrown physiologically during 

 voluntary activity. 



VI. Besides the motor reactions we must take into considera- 

 tion the inhibitory functions of the cortex, of which little is at 

 present known. 



The discussion in the last chapter of the effects of cerebral 

 extirpation shows that the fore-brain possesses inhibitory functions. 

 Goltz' brainless dog, which moved constantly in its cage so long 

 as it was awake and not overcome by fatigue and sleep, reminds us 

 of the continuous movement characteristic of certain forms of 

 dementia. This abnormal and aimless work may be regarded as a 

 natural effect of the loss of the inhibitory powers of the brain. In 

 agreement with this is the fact observed by Goltz that a whole 

 series of special characteristic reflexes can be evoked in the brain- 

 less dog, which are not obtained with the same promptness, facility, 

 and constancy in the normal dog (in which the brain is capable of 

 inhibition). We have seen that the ablation of the cerebrum in 

 mammals at first produces a state of rigidity or tonic contraction 

 in certain muscular groups of the trunk and" limbs which is au 

 exaggeration of the normal muscular tone, reflexly produced by 

 influences which reach the centres by the ordinary afferent paths 

 and are transmitted to the muscles by the motor paths. We saw 

 that after section of one side of the brain-stem the exaggeration of 

 tone and rigidity is produced in one half of the body only, because 

 it is only in one half that the inhibitory influence of the higher 

 centres, which normally moderates the reflexes that determine the 

 tone of the muscles, is lost. 



It is evident that the inhibitory influence of the brain may be 

 exercised by the will, as well as its excitatory function. We are 

 able at will not only to throw muscles into contraction, but also 

 to restrict or arrest their activity. We continuously exert a 

 regulating control over our reflex movements when we are awake ; 

 we are able to reinforce, moderate, or even arrest them. Does 

 this inhibition depend on the interruption of the activity of the 

 cortical motor centres, or on a positive activity which opposes the 

 impulses of these centres and suppresses their effects ? What is 

 the mechanism of this inhibition ? Are there in addition to the 

 motor centres and nerves other inhibitory cortical centres and 

 nerves ? Or are the same motor mechanisms capable of two 

 opposite forms of excitation ? These questions are entirely sub 

 judice, for it is possible to offer different solutions of them, with 

 experimental evidence in support of each. We must confine 

 ourselves here to recording the best-established facts. 



Bubnoff and Heidenhain (1881), after they had determined the 

 motor area in the dog, recorded the contractions of the extensor 

 muscle of the toes on a revolving cylinder. Any strong excita- 

 tion of the foot throws this muscle into reflex contraction. If, 



