156 ANIMAL CHEMISTRY LECTURE VI. 



medicinal efficacy of alterative salts. But when we remember 

 that every change produced in the composition of any part of the 

 animal body is a chemical change, necessitating a correlative 

 change in the composition of the reacting substance, it is obvious 

 that we must look for alterative agents among that class of sub- 

 stances which are most susceptible of chemical change ; and I 

 would add further, that an explanation of the different kinds of 

 alterative effect producible by different classes of compounds, as 

 of mercury and iron, for instance, is, doubtless, to be sought for 

 in the different chemical habitudes of the respective elements. 



(163.) A few words upon the effect of alkalies in promoting 

 oxidation. I mentioned in my last lecture the peculiar decom- 

 position of animal substances resulting from their treatment with 

 caustic alkali, and consisting in an oxidation of their carbonous 

 at the expense of their hydrogenous constituents. Now, this 

 action is apparently determined by the tendency which exists 

 among differently characterised elements to arrange themselves in 

 stable groupings, and more particularly to form stable oxi-salts. 

 The presence of alkali rendering the formation of such salts pos- 

 sible, by furnishing the necessary base, we find that under treat- 

 ment with caustic potash KHO, for instance, the carbon of organic 

 matter is oxidised into various acids, which appear in the form of 

 their respective potassium-salts ; while the excessive hydrogen of 

 the organic matter, together with that of the potash employed, is 

 liberated in the gaseous state, as already exemplified by the re- 

 action of caustic potash with oil of bitter almonds. As a 

 result of this tendency, then, we obtain, as I have previously 

 remarked, very similar products by fusing animal substances with 

 caustic alkalies, and by submitting them to the action of powerful 

 oxygenants. It is observable, however, as well in artificial as in 

 natural processes, that the ultimate effects of a gentle chemical 

 action are often more complete than the immediate results of a 

 comparatively violent one ; and it is to this more gentle action 

 of alkalies that I would now direct your attention. We find that 

 many organic substances, which of themselves are scarcely affected 

 by exposure to oxygen or air, undergo a complete and even some- 



