6 94 NERVOUS SYSTEM. 



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 inca- 

 pable 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 numerous experi- 

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

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

 firmed. Although the methods employed by Terrier were less delicate and accurate than 

 those of the German observers, the results obtained are of great value. Many other 

 physiologists have since confirmed the essential points developed in the original in- 

 vestigations ; 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 localized experi- 

 mentally 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 muscular con- 

 traction had no effect. It is evident that the section of the brain-substance would neces- 

 sarily 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 experimen- 

 tal 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 

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

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

 It comprehends, it is true, the facts deduced from experiments upon living animals, but 

 the results obtained by this method are comparatively few and their scope is restricted. 

 Nevertheless, they are sufficiently definite ; and, if these results be corrected and applied 

 to the human subject by a comparison with pathological facts, there still remains in psy- 

 chology much that may be regarded as within the range of experimental physiology ; for 

 pathological cases are very frequently available to the physiologist as accidental experi- 

 ments indicating the functions of parts of the human organism. We cannot restrict 

 ourselves, however, to this method in the study of the intellectual phenomena ; and we 

 must draw upon facts in comparative anatomy and physiology, anthropology, and, finally, 

 upon the direct observation and classification of the intellectual processes. 



The experimental physiologist has shown that the encephalon may receive impressions 



