GENERAL SUMMARY. 89 



all that are concerned in the maintenance of the organic functions, have an 

 obvious design, when considered either in their immediate effects, or in their 

 more remote consequences. The character of adaptiveness, then, in muscular 

 movements excited by external stimuli, is no proof that they are performed 

 in obedience to sensation ; much less, that they have a voluntary character. 

 In no case is this adaptiveness more remarkable than in some of those purely 

 instinctive actions which are not only performed without any effort of the will, 

 but which the will cannot imitate. This is the case, for example, with the act 

 of deglutition ; the muscles concerned in which cannot be thrown into contrac- 

 tion by a voluntary impulse, being stimulated only by impressions conveyed 

 from the mucous surface of the fauces to the medulla oblongata, and thence 

 reflected along the motor nerves. No one can swallow, without producing an 

 impression of some kind upon this surface, to which the muscular movements 

 will immediately respond. Now it is impossible to conceive any movements 

 more perfectly adapted to a given purpose than those of the parts in ques- 

 tion ; and yet they are not only independent of volition, but of sensation, being 

 still performed in cases in which consciousness is completely suspended, or 

 entirely absent. 



107. There is much difficulty, then, in ascertaining the really elementary 

 functions of the Nervous system, by experiments upon animals ; and it is only 

 when their results are corrected and explained by pathological observation on 

 Man, the sole case in which we can obtain satisfactory evidence of the pre- 

 sence or absence of sensation, that they have much value to the physiological 

 inquirer. From these combined sources, however, a vast amount of know- 

 ledge of the functions of the nervous system has recently been gained ; and 

 the general purposes to which it is subservient may be advantageously stated 

 in a systematic form, before we enter upon any detailed examination of them. 



I. The Nervous System receives impressions, which, being conveyed by 

 its afferent fibres to the sensorium, are there communicated to the conscious 

 mind. It is subservient in some way to the acts of that mind ; and, as the 

 result of these acts, a motor impulse is transmitted along the efferent trunks 

 to particular muscles, exciting them to contraction. This motor impulse, 

 however, may be either of an emotional or a voluntary character. We shall 

 hereafter see reason to believe that, to these functions, the Encephalon, and 

 the nerves proceeding from it, are subservient. 



II. Certain parts of the Nervous System receive impressions which are 

 propagated along afferent fibres, that terminate in ganglionic centres distinct 

 from the sensorium; and in these a reflex motor impulse is thus excited, 

 which, being conveyed along the efferent trunks proceeding from them, 

 excites muscular contraction, without any necessary intervention of sensation 

 or volition. Of this function (called by Dr. Hall, to whom the discovery of it 

 is in great part due, the reflex function), we shall find that the portion of the 

 Spinal, Cord of Vertebrata, which is not continuous with the fibrous structure 

 of the brain, together with the portion of the nervous trunks which are con- 

 nected with it alone, is the instrument. 



III. Another division of the Nervous System appears to have for its object, 

 to combine and harmonize the muscular movements immediately connected 

 with the maintenance of organic life, and to bring these into relation with 

 certain conditions of the mind. There is reason to believe (though this is less 

 certain) that it also influences, and brings into connection with each other, the 

 processes of nutrition, secretion, &c. ; though these, like the muscular move- 

 ments just mentioned, are essentially independent of it. 



108. Now, in reference to the first class of operations, it is well to explain 

 that, though the physiologist speaks of the intellectual powers, moral feelings, 

 &c., as functions of the Nervous System, they are not so in the sense in which 



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