18 MECHANICAL AND I.MMECHANICAL PARTS 



they are, yield to its powerful pervasion. The change 

 wrought by it is different from any chemical solution which 

 we can produce, or with which we are acquainted, in this 

 respect as well as many others, that, in our chemistry, par- 

 ticular menstrua act only upon particular substances. Con- 

 sider, moreover, that this fluid, stronger in its operation 

 than a caustic alkali or mmeral acid, than red precipitate 

 or aqua fortis itself, is nevertheless as mild, and bland, and 

 inoffensive to the touch or taste, as saliva or gum water, 

 which it much resembles. Consider, I say, these several 

 properties of the digestive organ, and of the juice with 

 which it is supplied, or ratiier with which it is made to sup- 

 ply itself, and you will confess it to be entitled to a name, 

 which it has sometimes received, that of *' the chemical 

 wonder ol animal nature." 



Still we are ignorant of the composition of this fluid, and 

 of the mode of its action ; by which is meant that we are 

 not capable, as we are in the mechanical part of our frame, 

 of collating it with the operations of art. And this I call 

 the imperfection of our chemistry ; for, should the time ev- 

 er arrive, which is not perhaps to be despaired of, when we 

 can com(>f)und ingredients, so as to form a solvent, which 

 will act in the manner in which the gastric juice acts, we 

 may be able to ascertain the chemical principles upon 

 which its efficacy depends, as well as from what part, and 

 by what concoction, in the human body, these principles 

 are generated and derived. 



In the meantime, ought that, which is in truth the de- 

 fect of our chemistry, to hinder us from acquiescing in the 

 inference, which a production of nature, by its place, its 

 properties, its action, its surprising efficacy, its invaluable 

 use, authoris'^s us to draw in ret^pect of a creative design? 



Another most subtle and curious function of animal bod- 

 ies is secretion. Tiiis function is secni-chemical and semi- 

 mechanical ; exceedingly important and diversified in its 

 effects, but obscure in its process and in its apparatus. 

 The importance of the secretory organs is but too well at- 

 tested by the diseases, which an excessive, a deficient, or a 

 vitiated secretion is almost sure oi producing. A single 

 secretion being wrong, is enough to make life miserable ; 

 or sometimes to destroy it. Nor is the variety less than 

 the importance. From one and the same blood (I speak 

 of the human body) about twenty different fluids are sepa- 

 rated ; in their sensible properties, in taste, smell, colour, 

 and consistency, the most unlike one another that is possi- 



