CHEMICAL BASIS OF THE ANIMAL BODY. 75 



t 



Chemical action is in all cases accompanied by an evolution or absorption of heat, 

 and it will add to the completeness of this account of the ferments if we consider 

 briefly the heat-phenomena which accompany the chemical action due to the 

 enzymes. Liebig regarded the fermentative decomposition of sugar as necessitating 

 a considerable consumption of energy, which he supposed to be derived from the 

 decomposing albumin of the ferment-substance. Hoppe-Seyler on the other hand 

 put forward the general view that heat is evolved in every case of ferment action, 

 basing it upon experiments in which he observed a distinct rise of temperature 

 during the action of pancreatic extracts upon starch, but more particularly upon the 

 opinion that the heat of combustion of the products of zymolysis is in all cases less 

 than that of the original substance from which the products have been formed 1 . 

 And this is undoubtedly the correct view. In addition to Hoppe-Seyler other 

 observers have observed a rise of temperature during zymolysis, e.g. in the case of 

 the formation of fibrin 2 , the clotting of milk 3 , and the inversion of cane-sugar 4 . 

 Maly on the other hand observed a considerable absorption of heat during the action 

 of pepsin on proteids and ptyalin on starch 5 . These experiments it may be 

 observed are discordant, and in reality they neither speak strongly for nor against 

 the evolution of heat during the action of the enzymes ; as a matter of fact they 

 could scarcely be expected to do so, since it is extremely difficult to make allowance 

 for the heat which may be simply absorbed or set free as the result of the varying 

 solubilities of the original substance and the products of its decomposition. The 

 real proof of the correctness of Hoppe-Seyler's view is the fact, already stated, that 

 the heat of combustion of the products of zymolysis is less than that of the 

 substance from which they are derived 6 . 



NITROGENOUS NON-CRYSTALLINE BODIES ALLIED TO PROTEIDS. 



These resemble the proteids in many general points, but exhibit 

 among themselves much greater differences than do the proteids. As 

 regards their molecular structure nothing satisfactory is known. Their 

 percentage composition approaches that of the proteids, and like these 

 they yield, under hydrolytic treatment, large quantities of leucin and in 

 some cases tyrosin. They are all amorphous. 



1 Med.-Chem. Unters. Hft. 4, 1871, S. 574. 



2 Lepine, Gaz. med. Paris, 1876. No. 12. 



3 Mayer, Milchzeitung , 1881, No. 2, 3, 4, 6. See Abst. in Maly's Bericht. 1880, 

 S. 209. But see also Musso, Ibid. 1879. S. 16. 



4 Kunkel, Pfliiger's Arch. Bd. xx. 1879, S. 509. But see Nageli, Ibid. Bd. xxn. 

 S. 310. 



5 Pfliiger's Arch. Bd. xxn. (1880), S. 111. 



6 For heat of combustion of physiologically important substances see Kechenberg, 

 Inaug. Diss. Leipzig, 1880, and Jn. f. prakt. Chem. (N.F.) Bd. xxn. (1880), Sn. 1, 

 223. See also Stohmann, Ibid. Bd. xxxi. (1885), and Landwirth Jahrb. Bd. xm. S. 

 513. Kubner, Zt. f. Biol. Bde. xix. (1883), S. 313 ; xxi. Sn. 250, 337. Berthelot 

 et Andre", Compt. Rend., T. ex. (1890), p. 884. 



