I08 ANIMAL CHEMISTRY LECTURE V. 



appreciate in its fullest extent what may be termed the mystery 

 of life, but they look upon the physiologists 1 explanation as a 

 mere periphrasis, as only another mode of saying that dead 

 matter differs from living matter because it is dead, while living 

 matter differs from dead matter because it is alive. Chemists and 

 physicists are well assured that, be life what it may, it is not a 

 generator, but only a transformer, of external force. In the 

 vegetable kingdom solar force is absorbed in the production of 

 our food ; in the animal kingdom it is liberated by the erema- 

 causis of our fat and glands and muscles. 



(115.) Now, the full realisation of the force derivable from a 

 given weight of muscle depends upon its complete oxidation into 

 water and carbonic acid or urea. Should it be only converted 

 into sugar, or kreatine, or uric acid, these are imperfectly burned 

 substances, which still retain a certain amount of potential energy 

 liberable from them by a further oxidation. They still have 

 associated with them some portion of the latent force put into the 

 original tissue-constituents at the period of their formation ; and 

 accordingly, by their further oxidation, we are capable of getting 

 an additional amount of work out of them. In order, therefore, 

 to obtain the full equivalent of heat-force or motive force to which 

 we are entitled by the waste of our tissues, it is important that 

 this waste should be thorough, that both the hydrogen and carbon 

 should be converted into the most completely oxidised compounds 

 they are susceptible of forming, the whole of the hydrogen into 

 water, and the whole of the carbon into its most stable mono- 

 carbon compound, namely, carbonic acid, or the ammoniated form 

 of that acid, namely, urea. In some cases of imperfect oxidation, 

 however, we get less oxidised, and more complex, dicarbon mole- 

 cules produced, such, for example, as oxalic acid, which occurs 

 either in its normal saline state, or colligated with urea in the 

 forms of allantoine, oxaluric acid, &c. In cases of yet more im- 

 perfect oxidation, we meet with still less oxidised tricarbon mole- 

 cules, such, for example, as the mesoxalic compound which, by its 

 colligation with urea, forms uric acid. We may even have tetra- 

 carbon molecules such as succinic acid, pentacarbon molecules 



