146 ANIMAL CHEMISTRY LECTURE YI. 



quate pulmonic oxidation of the blood of birds, not entirely com- 

 pensated for by its considerable systemic oxidation ; and how far 

 upon the connection with the portal circulation and inferior type 

 of structure of their kidneys, as well as upon the small amount of 

 water they drink and discharge, whereby their blood is less con- 

 stantly and thoroughly washed than is the blood of mammals, 

 are questions which it is for the physiologist rather than the 

 chemist to determine. 



(154). I can scarcely venture to conclude this course of lec- 

 tures on ' Animal Chemistry ' without saying a few words upon 

 the influence exerted on tissue-metamorphosis by those chemical 

 agents which are usually included in the class of alterative 

 medicines. Although our acknowledged ignorance of the mode 

 in which medicines produce their effects is made a standing 

 reproach to medical art, only by those who, ignorant of their 

 ignorance, wrongly conceive that in other scientific arts that of 

 the chemist, for example the use of the different agents em- 

 ployed has really ceased to be empiric, and become dependent 

 upon abstract principle, still it will not do for us to regard the 

 therapeutic actions of different medicines as ultimate facts with 

 which we must ever rest contented, but rather as difficult pro- 

 blems inviting a more competent investigation, and destined 

 some day or other to yield to our inquiries. The subject, how- 

 ever, is too remote from even the present widely-extended boun- 

 dary of scientific knowledge the path from the known to the 

 unknown is yet too lengthy and intricate to warrant us in ex- 

 pecting any immediate, or, indeed, proximate resolution of the 

 darkness by which it is surrounded. In the belief, however, 

 that even a little gleam of light, insignificant in relation to more 

 advanced researches, may not prove altogether worthless here, I 

 beg respectfully to suggest the following points for your con- 

 sideration. It will be found, I think, that those mineral sub- 

 stances which act more especially as alteratives, actually are, and 

 necessarily ought to be, characterised, not by their chemical 

 energy, but by their chemical mobility ; and I do not know that 

 I can make my meaning better evident than by directing your 



