56 THE BUTYRIC ACID GROUP. 



As we proceed in the subject of zoo-chemistry we shall become 

 acquainted with a number of bodies whose characteristic properties 

 are so feebly marked that it is only by an elementary analysis 

 that we can satisfy ourselves regarding their presence. Often as 

 the combustion-tube may have been mis-used in physiological 

 chemistry, we are yet convinced that no one can flatter himself 

 that he will advance zoo-chemistry and physiological chemistry, 

 if he be not conversant with the methods of elementary analysis 

 as now practised. It has unfortunately happened that physio- 

 logical chemistry has too long remained in the hands of chemical 

 dilettanti, who looked upon an elementary analysis as a great piece 

 of art, and have based on the elementary analyses of others those 

 lamentable fictions which, even yet, have hardly been eradicated 

 from physiological chemistry. 



Physiological Relations. 



Occurrence. Since acids homologous to metacetonic acid have 

 so frequently been found in the animal system, at least as products 

 of decomposition, we may rationally suppose that this acid may, 

 at least occasionally, occur in pathological conditions of the 

 organism; to this we may add that, on the one hand, metacetonic acid 

 is, in its chemical composition, very closely allied to lactic acid, 

 which is of such frequent occurrence in the animal body (for with 2 

 atoms of oxygen metacetonic acid yields lactic acid : C 6 H 5 O 3 .HO 

 + 2O = C 6 H 5 O 5 .HO), and that on the other glycerin, (of which 

 we are ignorant what becomes of it in the decomposition of the 

 fats in the animal body) is so readily converted into metacetonic 

 acid (for C 6 H ? O 5 - HO=C 6 H 5 O 3 . HO); but, unfortunately, 

 metacetonic acid has been only so recently known to chemists, 

 that little or no search has as yet been instituted for it in the 

 animal organism. 



BUTYRIC ACID. C 8 H 7 O 3 . HO. 



Chemical Relations. 



Properties. This acid is an oily fluid, which remains in that 

 state at a temperature of 20, and can only be solidified at a cold 

 of 113 induced by mixing condensed carbonic acid and ether, 

 when it crystallises in plates ; it evaporates even at the ordinary 

 temperature, but it does not boil at a lower temperature than 



