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PHYSIOLOGY. 



PHYSIOLOGY. CEEEBEAL LOCALIZATION. 

 Dr. Sigmund Exner has proposed a new sys- 

 tem of cerebral localization, in which, instead 

 of depending on experiments upon animals 

 and the application of the results to the hu- 

 man brain, he fixes the seats of the several 

 functions of the brain by deduction from the 

 results of autopsies, and the light they throw 

 on the relations of disease and the brain. The 

 localizations as determined in his system agree 

 generally as to their main features with those 

 fixed by Dr. Ferrier from his experiments upon 

 animals, but with some differences in detail. 

 Dr. Exner distinguishes between absolute areas 

 or centers of action, lesion of which always 

 causes the same symptom, and relative areas 

 or centers, lesion of which does not always, 

 but only frequently, cause affection of the 

 function with which they are supposed to be 

 in relation ; and he admits that the centers or 

 areas of different organs, instead of being sharp- 

 ly defined and separated, run into each other, 

 and are even partly inclosed one within an- 

 other. In regard to the last point, he has re- 

 marked, in defending his opinions against criti- 

 cisms by Professor Terrier, that " there is no 

 fact that would support the opinion that the 

 part designated in the cortex as centrum has 

 no other function than the one which caused 

 it to be called ' centrum ' ; neither is there any 

 fact which would support the idea that these 

 centers are sharply circumscribed, that the or- 

 gan of the leg extends, as on a map, as far as a 

 designated limit, on which another organ be- 

 gins. Anatomy and histology of the cortex, 

 which teach that from every part of it fibres 

 in immense quantities break through into the 

 neighboring areas, are decidedly against such 

 a view; and it is the result of preconceived 

 opinion when every case is considered obscure 

 and rejected in which, in spite of the lesion 

 being very small, there were motor disturb- 

 ances in both extremities. I consider a view 

 based on such principles, according to which a 

 ' centrum,' recognized as ' motor centrum,' can 

 only have connection with the muscle group 

 belonging to it, and with nothing else, as an hy- 

 pothesis which prevents an impartial research. 

 ... I have proved . . . that from the greater 

 part of the cerebral cortex (visible from above) 

 of the rabbit we can call forth movement in 

 both fore paws by electric irritation, and that 

 these movements are transmitted by fibres 

 which penetrate from the cortex into the 

 white substance of the hemispheres." 



PHYSIOLOGY OF EXERCISE. Professor Du 

 Bois-Reymond has shown, in an address on the 

 "Physiology of Exercise," before the Institute 

 for Military Surgeons, at Berlin, how the func- 

 tions of exercise are much more extensive than 

 has been popularly supposed, and how that ex- 

 ercise may stand in intimate connection with 

 natural selection as a factor in the improve- 

 ment of the higher animals and races. Having 

 described the generally known effects of exer- 

 cise in facilitating certain movements, harden- 



ing the tissues and developing glands, and in 

 making the system more secure against certain 

 kinds of injury, he gives, as the broader defini- 

 tion of the term exercise, the frequent repeti- 

 tion of a more or less complicated action of the 

 body with the co-operation of the mind, or of 

 an action of the mind alone, for the purpose of 

 being able to perform it better. Exercise has 

 generally been spoken of in connection with 

 the body only, or with the muscular system ; 

 but " it is easy to show the error of this view, 

 and to demonstrate that such bodily exercises 

 as gymnastics, fencing, swimming, riding, danc- 

 ing, and skating are much more exercises of 

 the central nervous system, of the brain and 

 spinal marrow." Every action of our body as 

 a motive apparatus depends more upon the co- 

 operation of the muscles than upon the force 

 of their contractions. In order to execute a 

 composite motion, the muscles must begin to 

 work in the proper order, and the energy of 

 each of them must increase, halt, and diminish 

 according to a certain law, so as to produce 

 the proper combination of positions and veloci- 

 ties. On this point Johann Mtiller has a perti- 

 nent remark, that improvement in exercises of 

 the body often consists nearly as much in the 

 suppression of unnecessary by-motions as in 

 acquiring dexterity in essential motions. Still 

 other faculties come into action in executing 

 these composite motions. The sight, the sense 

 of pressure, the muscular sense, and the mind 

 must be prepared to take in the position of the 

 body at each instant, so that the muscles may 

 be in a proper state of adjustment. Thus, not 

 only the motor, but the sensory nervous system 

 also, and the mental functions, are capable ot 

 being exercised, and need it ; and in all skilled 

 work, while muscular strength and facility are 

 absolutely necessary, the supreme essential is 

 the control by the central nervous system and 

 the mind. In all these processes, the more 

 any composite movement is practiced, the 

 more unconscious is the act of the nervous 

 system directing it, until at last the latter 

 can not be distinguished from spontaneous 

 nervous mechanisms like the involuntary re- 

 flex and by-movements. Practice further ex- 

 hibits its influence on the purely sensory side 

 of the nervous system, training the musical 

 ear, improving the local sense and the color 

 sense of the eye, and teaching such wonderful 

 arts as quick reading and the instantaneous 

 taking in of fleeting phenomena. As it in- 

 duces the discontinuance of unused muscles, it 

 also teaches us to neglect unused images; and, 

 as exercise refines the senses, neglect stupefies 

 them. 



Man is thus adapted to self-improvement by- 

 means of exercise. "It makes his muscles 

 stronger and more enduring ; his skin becomes 

 fortified against all injury ; through exercise 

 his limbs become more flexible, his glands 

 more productive. It fits bis central nerve- 

 system for the most complicated functions ; it 

 sharpens his senses, and by it his mind, react- 





