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M A M M A L I A. 



diseased action. Irritation or pressure will produce 

 these results : and this would lead us to conclude 

 that all sensation is ultimately resolvable into some 

 suspension or change of the general motions or 

 actions which are continually going on in the very 

 complicated structure of the animal ; and that the 

 sensation, whether its immediate cause is external or 

 internal, is extensive in proportion to the extent of 

 this resistance. We have a very clear proof of this 

 in those cases in which both men and animals are 

 panic-struck by appearances or impressions of any 

 kind upon the senses, which are not only not danger- 

 ous in themselves, but which under another previous 

 state of the system would be regarded with perfect 

 indifference, and probably with pleasure. 



The most interesting, but at the same time the 

 most difficult, portion of this branch of physiology is 

 that which treats of sensations that lead to action in 

 the animal. In the mammalia, and in other animals 

 not endowed with mind, the reciprocating principle, 

 which as it were transfers the sensation to action, is 

 called an instinct, and this instinctive mode of action 

 prevails also in man, and the form of it is put on after 

 long hubit, in many cases of which the first instances 

 are the undoubted results of mental inquiry and de- 

 termination, upon judgment formed according to the 

 evidence. From the difficulty already mentioned as 

 arising from our inability so to analyse our sensations, 

 or rather the impressions we receive, into the animal 

 part and the mental part, and this additional difficulty 

 produced by the merging of processes once mental, in 

 habits merely animal or little else, render this an 

 almost inexplicable part of animal physiology. Many 

 hypotheses have been formed for the purpose of ex- 

 plaining it ; and as in these hypotheses structures 

 have been endowed with gratuitous or imaginary 

 functions to make them agree with the phenomena, 

 there is some plausibility in every hypothesis of this 

 kind, but it is impossible to say that there is philoso- 

 phic truth in any of them. One of the most com- 

 monly received of these hypotheses has been that of 

 two sets of nerves, one of them originating in the 

 brain and its spinal continuation, and ramifying thence 

 to all the surfaces and terminal parts of the body, 

 where their extremities, furnished with certain struc- 

 tural apparatus, such as papilla; for touching and 

 tasting, and more complicated structures for hearing 

 and seeing, stand as sentinels there, and send word 

 of whatever is going on to the great central mass of 

 nervous matter, which, according to the hypothesis, 

 is the sensorium or seat of instinct in the irrational 

 animal, and of instinct and mind jointly in man. It 

 is to be understood that this is perfectly gratuitous, 

 or that at all events the alleged functions have been 

 invented or shapen so as to suit the phenomena 

 which are said to arise from their exercise ; but there 

 is a business-like mechanical detail about it, and 

 therefore it has never been without numerous and 

 devoted adherents. 



But before any novice takes it up dogmatically, he 

 would do well to consider that we are, and are likely 

 for ever to remain, in perfect ignorance of the prin- 

 ciple which moves the smallest fibre of the most deli- 

 cate muscle in its contraction ; and as this sensorium 

 is a structure of many " stories,'' resting upon the 

 supposed knowledge of this power of action in the 

 muscular fibres as its very first foundation, it cannot 

 surely have much more philosophical stability than 

 that upon which it is presumed to rest. 



It may not be amiss to notice the second or TP 

 versed part of this supposed communication, between 

 the nerves which are ramified through the organs 

 more immediately concerned in action and the sen- 

 sorium. The course is the opposite of the former, 

 according to the hypothesis, but not necessarily by 

 the same means, as the perception and the action 

 may not be performed by the same parts. It may, 

 for instance, be the sight of a hare by a greyhound 

 or other dog, and the following of that hare in the 

 chace ; or it may be any other sensation, and any 

 other action ; but there is always understood to be 

 an informing of the sensorium, which is not supposed 

 to have in itself any direct knowledge of the external 

 world, or even of the internal structure or action of 

 the body of the animal ; but which nevertheless 

 always decides whether action shall or shall not fol- 

 low the deliberation on the evidence, and in what man- 

 ner and to what extent the action shall be carried on. 



All this is done too by means of organisation in 

 the sensorium ; and the different parts of this organ- 

 isation affect the result differently, according to their 

 different degrees of development and consequent 

 power. Thus a village cur, with short bandy legs 

 and a wriggling body, sees a hare as well as the grey- 

 hound did. His organ of acquisitiveness is instantly 

 roused, and oft' he waddles, losing on the hare at 

 every step, because his organs of locomotion will not 

 obey the full bent of the acquisitive organ. Thus, in 

 him at least, we have the effort of the sensorium 

 foiled by the stubborn resistance of the external 

 organs. Innumerable cases of a similar nature might 

 be mentioned, in which it is impossible to impute the 

 success or failure of the action, or even the com- 

 mencement of it, to any thing but the general 

 structure and present circumstances of the animal, 

 and this casts much doubt upon the whole hypothesis. 

 But the whole case as it applies to the mummnlia, 

 and by necessary consequence to all the lower classes 

 of animals, must necessarily be explained upon animal 

 principles alone, without the slightest reference to 

 any thing mental ; and this notion of a sensorium, 

 consisting of a certain portion of the animal's organ- 

 isation, which receives the impressions of the senses 

 either from the local organs of particular named 

 senses, or from the general sensibility of the animal ; 

 and then, after duly understanding the impression so 

 brought, puts the organs of action in motion, accord- 

 ing as the result of its judgment may be, is really 

 endowing the animal with an intellectual principle or 

 mind, whatever name may be given to it. 



The author of this article does not believe that the 

 source of action in animals, even of that kind which is 

 consequent to sense or perception, can be shown to 

 have its seat in the brain any more than in other parts 

 of the structure. That the brain is the central mass of 

 the nervous system, and that it supplies nerves to the 

 organs of the allocated senses, which are, for conveni- 

 ence of use, situated in the head of all the mammalia, 

 is perfectly true ; and it is equally true, though the 

 particulars are much more obscure, that a healthy 

 state of the nerves is necessary in order to make those 

 organs perform their functions properly. This, how- 

 ever, proves nothing as to any exclusive possession of 

 the faculty of sensation, and of the stimulus to action 

 in the nerves ; for a healthy state of the blood vessels, 

 and even of the lymphatics, is just as essential to the 

 proper functions of the organs of the senses as a 

 healthy state of the nerves. We have an instance of 



