694 NERVOUS SYSTEM. 



responded to a feeble galvanic current. Each galvanization produced movements re- 

 stricted to certain muscles, and 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 abductor mus- 

 cles of the forelegs ; and so on, other centres for sets of muscles being found in the an- 

 terior portion of the hemispheres. By passing an interrupted current 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 corresponding to the centres operated upon. In 

 these experiments the action was always crossed. It was also found that, after severe 

 hemorrhage, the excitability of the cerebrum quickly disappeared, which may account 

 for the negative results obtained by previous experimenters. No motor properties were 

 discovered in the posterior portion of the cerebrum. 



The experiments just cited throw a new light upon the properties of the cerebral 

 substance. It has always been found difficult to experiment upon the great encephalic 

 centres without disturbing the physiological conditions so seriously as to render the 

 results of direct observations of this kind more or less indefinite. Now that it is ascer- 

 tained that, in all probability, these centres readily lose their normal properties, as a sim- 

 ple consequence of hemorrhage and exposure of the parts, we are less disposed to accept 

 the older experiments, in which the cerebral tissue was apparently shown to be incapable 

 of receiving direct artificial impressions. 



Since the first publication of the remarkable experiments to which we have just 

 referred, the question of the excitability of certain parts of the cerebral hemispheres has 

 attracted a great deal of attention and has been made the subject of many experi- 

 ments. The most notable of the later observations on this subject are those of Ferrier, 

 of London, by whom the original experiments of Fritsch and Hitzig have been fully con- 

 firmed. Many other physiologists have since confirmed the essential points developed in 

 the original investigations; and the only serious objection to the results is the possibility 

 of diffusion of the galvanic current to recognized motor tracts. This question is pretty 

 well settled by the following experiment made by Dr. Putnam, of Boston: Having local- 

 ized experimentally a distinct motor centre on the surface of the brain, he made a flap, 

 about one-twelfth of an inch thick, by a section parallel to the surface of the brain and 

 involving this centre. With the flap in situ, the current which had before excited mus- 

 cular contraction had no effect. It is evident that the section of the brain-substance 

 would necessarily cut off the physiological conduction of a stimulus; but, with the 

 flap in situ, the section would probably not interfere with the diffusion of the galvanic 

 current itself. 



In the present condition of the question, the above is all that it seems necessary to 

 say, in a systematic work upon physiology, concerning the excitable centres of the cere- 

 brum. That these excitable centres exist, there can be little doubt; and the idea that 

 the movements produced by their galvanization are reflex is not justified by experimental 

 facts. These observations have been confirmed by Hitzig as late as in 1874; and his last 

 experiments fully substantiate the views advanced in his first paper, showing loss of 

 power in certain muscles, following destruction of portions of the brain-substance cor- 

 responding to the excitable points. 



functions of the Cerebrum. 



The history of the functions of the encephalon belongs without question to physiol- 

 ogy and is one of the most extensive and interesting of the subdivisions of the science ; 

 but its range is so extensive, that it has long been regarded as a science by itself and is 

 treated of exhaustively only in special treatises upon psychology. The study of psychology 

 has been pursued by the method of observation much more than by direct experiment. 



