GENERAL SUMMARY. 657 



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

 animals made the subjects of experiments; and in the interpretation of these, 

 great caution must be exercised. 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 ( 674). Further, we are not justified in 

 assuming that Consciousness is excited by an irritation, still less that Intelli- 

 gence and Will are called into exercise by it, merely because movements, 

 evidently tending to get rid of its source, are performed in respondence to it. 

 We know that the contractions of the heart and alimentary tube are ordinarily 

 excited by a stimulus, without any sensation being involved ; and these move- 

 ments, like 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 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 ( 427, 428), 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 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 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. The act of Sucking in the infant, again, is one in which a number of 

 muscles are called into combined contraction, in a manner which shows a most 

 complete adaptation to a given purpose ; &nd yet it is impossible to suppose 

 this adaptation to be purposive on the part of the infant itself ; more especially 

 as it is shown, both by the occurrence of monstrosities, and by experiments 

 made with this object ( 423), that no part of the Cranio-spinal axis above the 

 Medulla Oblongata is necessary to it. And in the acts of Coughing and 

 Sneezing ( 555), we have examples of the most adaptive movements, executed 

 by a marvellous combination of separate muscular actions, with the obvious 

 purpose of removing a source of irritation from the air-passages ; and yet we 

 know by personal experience, that this combination is not made with any design 

 of our own. 



695. In addition to the Cerebro-Spinal system of ganglionic centres and 

 nerve-trunks, all but the lowest Vertebrated animals possess a system of 

 ganglionic centres scattered in different parts of the body, but mutually con- 

 nected with each other, as well as with the Cerebro-spinal system ; this is com- 

 monly termed the Sympathetic system; but not unfrequently, from the 

 position of its principal centres, and their evident functional relation to the 

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