TO PHYSIOLOGY AND PATHOLOGY. 39 



EXAMPLES. 



Examples of this assertion can be found in every physiological work ; and I will 

 give a few illustrations from one of the most recent treatises. Valentin says,* 

 " We perceive on dividing the facial nerve, that the muscles of the face on the cor- 

 responding side are paralysed as far as the will is concerned. We thence justly 

 conclude that the effects of our will are communicated by means of the facial nerve 

 to the muscles of expression. 



" We find, after injury of the trunk, or the branch of the fifth pair of nerves 

 supplying the eye, that secondary inflammation, suppuration, and even further, 

 destruction of the globe of the eye, are occasioned ; and conclude, therefore, that 

 the integrity of the above-named nerves is necessary to the normal condition of 

 the eye." 



Further on, at page 3, we find as follows : " I know that the walls of the arteries 

 are elastic, and I may, therefore, at once conclude that they distend to a certain 

 extent as soon as they have been filled with blood ; and that on the yielding of the 

 pressure they return to their original circumference ;" that is to say, they are elastic. 



POINT OF CONTACT BETWEEN PHYSIOLOGY AND CHEMISTRY. 



I have shown in the above, how much the difference in the way of viewing 

 things, adds to the difficulty of arriving at an understanding between physiologists 

 and chemists ; and I will now endeavor to consider more particularly the point 

 of contact, at which physiology and chemistry ought to meet in order that they 

 may mutually assist each other. 



DEVIATION OF CHEMICAL AND MECHANICAL LAWS FROM THE 

 LAWS WHICH GOVERN VITAL PHENOMENA. 



If we endeavor to make use of illustrations derived from the knowledge of 

 mechanical forces, in the inquiry of vital or chemical phenomena, we immediately 

 observe that the laws which govern the former, differ in many respects from those 

 on which the peculiarities of chemical or vital combinations are dependent. 



RELATION OF THE PROPERTIES OF ELEMENTS TO THE PROPERTIES 

 OF THEIR COMBINATIONS. 



A chemical combination of two bodies, possesses properties which are entirely 

 different from those of its several constituents. The chemical force of the new 

 body, the power of entering into new combinations, or bringing about decompo- 

 sition, is not the sum of the chemical forces of its elements. We are entirely 

 unable, by tracing backwards, from the properties of a muscular fibre, to decide 

 concerning those of carbon, hydrogen, nitrogen, and its other elements ; and yet 

 nothing can be more true, than that certain relations remain permanent between the 

 properties of the elements, and those of their combinations. 



Cinnabar is a metallic sulphuret, which possesses totally different properties from 

 sulphuret of lead on sulphuret of zinc. It cannot be doubted that their difference 

 is dependant upon the fact of mercury being combined in the first, lead in the 

 second, and zinc in the third, with sulphur; and that the properties of the mercury, 

 lead, and zinc, must have an entirely definite and definable share in the difference 

 of the properties of their combinations, since the latter are evidently dependent 

 upon the difference. We see this the most clearly in the isomorphous substances ; 

 sulphuret of lead is scarcely, in appearance, to be distinguished from seleniuret of 

 lead, sulphate of alumina and ammonia, from sulphate of alumina and potash, 

 selenate of soda, from sulphate of soda. The relations which exist between the 



* Manual of Physiology, Brunswick, 1844. 



