628 EVOLUTION OP HEAT, LIGHT, AND ELECTRICITY. 



is easy to understand why it should possess its temperature. Many facts prove 

 that the degree of temperature and sensibility in a part are in direct ratio with 

 the amount of blood circulating in it. 



If galvanism be applied to the superior portion of the sympathetic nerve 

 after it has been cut in the neck, the vessels of the face and ear, after a short 

 time, begin to contract, and subsequently resume their normal condition, if they 

 do not even diminish. Coincidently with this diminution, there is a decrease of 

 the temperature and sensibility of the face and ear, until the palsied and sound 

 side are alike in this respect. 



When the galvanic current ceases to act, the vessels again dilate, and all the 

 phenomena discovered by M. Bernard reappear. It hence appears that the 

 only direct effect of section of the cervical portion of the sympathetic is the 

 paralysis and consequent dilatation of the bloodvessels. Another deduction 

 from these experiments is, that the sympathetic sends motor fibres to many of 

 the bloodvessels of the head. 1 ] 



663. The influence which conditions of the Nervous System are thus shown 

 to possess over the function of Calorification has led some Physiologists and 

 even Chemists to the conclusion that the production of Heat is essentially de- 

 pendent upon Nervous agency, of which it is one of the manifestations. But, 

 as Prof. Liebig justly observes, "if this view exclude chemical action, or changes 

 in the arrangement of the elementary particles, as a condition of nervous agency, 

 it means nothing else than to derive the presence of motion, the manifestation 

 of force, from nothing. But no force, no power, can come of nothing." 2 That 

 the production of heat in living bodies may take place without any possible 

 assistance from nervous agency, is manifest from the phenomena of Vegetable 

 heat already referred to (655) ; and there can be no reasonable doubt, that the 

 source of this production is a true combustive process. And the evidence afforded 

 by the post-mortem production of heat in the Human subject ( 652) conclu- 

 sively points to the same result; more particularly as the elevation of tempera- 

 ture observed in the brain was uniformly less than that which was manifested 

 in other large organs. But the phenomena just enumerated (and many others 

 that might be cited) can scarcely be accounted for, without admitting that the 

 Nervous system exerts an important modifying power upon the temperature of 

 the body, which may be either elevated or depressed through its agency ; and 

 the question now arises whether this operation takes place through the influence 

 which the Nervous system exerts over the molecular processes of Nutrition, Se- 

 cretion, &c., or through some more direct method. It can scarcely be denied 

 that the first of these channels affords not merely a possible, but also a probable 

 means, for the exercise of such influence; but still it is difficult to conceive 

 that any great effect can be thus produced, since, as already shown, it is not 

 so much in the growth as in the disintegration of textures, that heat is pro- 

 duced by the oxidation of their components. On the other hand, from the 

 close relation which has been shown to exist between the Vital and Physical 

 forces (CHAP. in. SECT. 2), -it can scarcely be regarded as improbable that the 

 Nervous force, generated by molecular changes in the Nervous substance, may 

 manifest itself under the form of Heat, just as we know that it manifests itself 

 (as in the Electric fishes) under that of Electricity. 3 And thus it is quite con- 

 ceivable that one mode in which alimentary materials may be applied to the 

 maintenance of Animal Heat, may consist in their subservience to these mole- 

 cular changes, which seem to take place in the Nervous substance with more 

 activity than in any other tissue; and thus a large measure of caloric may be 



1 Vide Phil. Med. Exam., N. S., vol. viii. No. viii., August, 1852. 



2 "Animal Chemistry," 3d edit., p. 39. 



3 See "Princ. of Phys., Gen. and Comp.," \\ 635-639, Am. Ed. 



