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THE POPULAR SCIENCE MONTHLY.— SUPPLEMENT. 



then recent investigations of Sir Charles Bell, 

 Marshall Hall, and others, had begun to eluci- 

 date the nature of sensation and motion as func- 

 tions dependent upon the properties and the in- 

 tegrity of the nervous system. It had long been 

 evident that the operations of the mind, what- 

 ever might be their original source in a higher 

 or spiritual nature, were recognizable as opera- 

 tions of the brain, which was, at any rate, the 

 immediate instrument of their performance ; and 

 it was soon perceived that all the modes of ac- 

 tivity of the nervous system, from the lowest to 

 the highest, were united in one continuous scries, 

 which could only be successfully investigated by 

 beginning with the simplest forms of their dis- 

 play, and by then tracing upward to the summit 

 the separate strands of an ever-increasing com- 

 plexity of structure, and the separate rudiments 

 of an ever-increasing variety of use. In this 

 work Dr. Carpenter was himself the pioneer, and 

 it was one of his first achievements, by the appli- 

 cation of comparative anatomy, or the study of 

 the nervous endowments of the lower animals, to 

 crumble the whole fabric of phrenology into dust. 

 He showed, in the British and Foriign Medical 

 Review for 1846, that the first rudiments of brain 

 found in ascending the animal scale were rudi- 

 ments of the anterior lobes, that the middle and 

 the posterior lobes were gradually added, that 

 the posterior lobes reached their full develop- 

 ment in man alone ; and hence that the hy- 

 pothesis which seated the intellectual qualities 

 in the anterior lobes, the moral qualities in the 

 middle lobes, and the animal propensities in the 

 posterior lobes, was in direct contradiction to 

 the unbroken order of Nature. In the same 

 article, the publication of which formed an epoch 

 in the history of nervous physiology, he estab- 

 lished cardinal principles, which he has since 

 done much to elucidate and to develop in the 

 successive editions of his great work on physi- 

 ology, and which, in the present treatise, he has 

 given to the world in the most finished form that, 

 in the present state of knowledge, they are capa- 

 ble of receiving. In order to render them even 

 partially intelligible it is necessary to endeavor 

 to sketch some outline of the essential conditions 

 under which nervous functions are performed. 

 In doing so, we are constrained by the exigencies 

 of space to limit ourselves to the most simple 

 statement, and must refer those who desire illus- 

 tration and elucidation to the pages of the book 

 which lies before us. 



The fundamental conception of a nervous 

 system is of a central body or ganglion, which is 



itself a seat of activity, and which receives an 

 "afferent" fibre from some remote part of the 

 body, and sends forth an " efferent " fibre to the 

 same or to some other part. The afferent fibre 

 conveys intelligence of some change occurring in 

 the external part in which it terminates ; the ef- 

 ferent fibre conveys from the centre an impulse 

 consequent upon that intelligence. All this, in 

 its essential nature, is independent of sensation 

 or of the knowledge of the animal, and is said, in 

 physiological language, to be automatic. In the 

 human body there are ganglia in the lower part 

 of the spinal cord, which receive afferent fibres 

 from the sole of the foot, and send out efferent 

 fibres to muscles which move the leg. The ac- 

 tions hence arising are usually the subjects of 

 consciousness, but this is only because the seat 

 or organ of consciousness is attending to them. 

 When there is disease limited to the middle part 

 of the spinal cord, but cutting off this part from 

 communication with the brain, and when the legs 

 of the patient are concealed from his sight by 

 the interposition of a screen, the essential inde- 

 pendence and the automatic character of the 

 spinal movements may be readily demonstrated. 

 If the sole of the foot is then tickled by a feather, 

 the tickling will produce an impression upon the 

 extremity of the afferent nerve. This impression 

 is conducted to the central ganglion, whence an 

 impulse is conveyed along the efferent nerve to 

 muscles of the leg, and the foot is drawn up or 

 moved away. Very violent action may often be 

 obtained in this manner, the patient feeling nei- 

 ther the tickling nor the movement, and remain- 

 ing unconscious of both. Such movements, which 

 are neither voluntary nor attended by sensation, 

 but are produced by the automatic response of 

 the simplest form of nerve-mechanism to the 

 stimulus of an " impression," are called "reflex." 

 In some of the lower forms of animal life the 

 fibres and ganglia necessary for reflex movements 

 are detached from one another, and distributed 

 irregularly about the body ; but in the class of 

 insects named Articidctta, of which the common 

 centipede may be taken as a good example, the 

 ganglia are united into an axial chain, which es- 

 sentially corresponds to the spinal cord of the 

 higher animals and of man. The purely reflex 

 character of many of the apparently " purposive" 

 or voluntary actions of the Articulaia was first 

 demonstrated by Dr. Carpenter in his "Inaugural 

 Dissertation" at Edinburgh for the degree of 

 M. D., which was published in 1839. His views 

 were at that time strongly opposed by Mr. New- 

 port, who became a convert to them four years 



