GENERAL PROPERTIES OF THE CEREBRUM. 323 



From the above facts, all physiologists of the present day 

 are agreed that a great part of the substance of the cerebrum 

 is neither excitable nor sensible, in the sense in which these 

 terms are applied to the ordinary mixed nerves. There can 

 be no doubt with regard to the conducting properties of the 

 white matter of the brain, but the nerve-fibres here seem to 

 conduct impressions conveyed to them by the sensory nerves 

 and the stimulus generated by the nerve-cells, without being 

 capable of receiving or conducting artificial impressions ap- 

 plied directly to their substance. 



We have said that a great part of the cerebral substance 

 seems to be neither excitable nor sensible to direct stimula- 

 tion ; but we must make an exception in favor of certain 

 portions of the cerebrum, which have lately been shown to 

 possess excitability, their action being confined to particular 

 sets of muscles. Fritsch and Hitzig, exposing the cere- 

 bral hemispheres in dogs, found that certain parts of its an- 

 terior portion responded to a feeble galvanic current. The 

 stimulation was applied by means of two needles, conducting 

 a feeble galvanic current, introduced through the gray into the 

 white substance. Each galvanization produced movements 

 restricted to particular sets of muscles ; but it was difficult to 

 say whether the contractions were due to stimulation of the 

 white or of the gray substance. Different centres for the 

 sets of muscles were accurately determined. The centre for" 

 the muscles of the neck was located in the middle of the 

 frontal convolution ; external to that,* was a centre for the 

 extensor and adductor muscles of the forelegs ; and so on, 

 other centres for sets of muscles being found in the anterior 

 portion of the hemispheres. By passing an interrupted cur- 

 rent through these parts, tetanus of particular muscles was 

 produced. In. other observations, when the gray substance 

 was removed at the points mentioned, there was partial loss 

 of power, but not paralysis, of the sets of muscles correspond- 

 ing to the centres operated upon. The authors regarded 

 this as due to a loss of " muscular sense." In these experi- 



