DETERMINATION OF FUNCTIONS OF NERVES. 245 



within ourselves, and that which we obtain from watching the manifestation's 

 of disease in Man, is derived from observation of the phenomena exhibited 

 by animals made the subjects of experiments; and it is desirable to preface 

 our general summary of the results of these, by some remarks upon the in- 

 ferences to be drawn from them. In the first place it must be constantly 

 borne in mind that, except through the movements consequent upon them, 

 we have no means of ascertaining, whether or not particular changes in the 

 Nervous System, whose character we are endeavoring to determine, are 

 attended with Sensation; since we have no power of judging whether or not 

 this has been excited, save by the cries and struggles of the animal made the 

 subject of experiment. Now although such cries and struggles are ordinarily 

 considered as indications of pain, yet it is not right so to regard them in every 

 instance; and the only unequivocal evidence is derived from observation of 

 the corresponding phenomena in the Human subject; since we can there 

 ascertain, by the direct testimony of the individual affected, what impressions 

 produce sensation, and what excite movements independently of sensation. 

 Further, we are not justified in assuming that consciousness is excited by an 

 irritation, still less that the intelligence and will are called into exercise by 

 it, merely because movements, evidently tending to get rid of this, are per- 

 formed in respondence to it. We know that the contractions of the heart 

 and alimentary tube are ordinarily excited by a stimulus, without any sensa- 

 tion being involved; and these movements, like all that are concerned in the 

 maintenance of the Organic functions, have an obvious design, when con- 

 sidered 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 sensa- 

 tion ; much less, that they have a voluntary character. In no case is this 

 adaptiveness more remarkable, than in some of those 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 contraction 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 

 the motor nerves. No one can swallow without producing an impression of 

 some kind upon this surface, to which the muscular movements will imme- 

 diately respond. Now it is impossible to conceive any movements more 

 perfectly adapted to a given purpose than those of the parts in question ; and 

 yet they are independent, not only of Volition, but of Sensation, being still 

 performed in cases in which consciousness is completely suspended, or 

 entirely absent. 



307. 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 observa- 

 tion on Man, the sole case in which we can obtain satisfactory evidence of 

 the presence or absence of sensation, that they have much value to the phy- 

 siological inquirer. From these combined sources, however, a vast amount 

 of knowledge 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, and thus give origin to Sensations. The Nervous structure is further 

 subservient, in some way, to the acts of that mind ; as the result of which, a 

 motor impulse is transmitted along the efferent trunks, to particular Muscles, 



