CHEMICAL BASIS OF THE ANIMAL BODY. 129 



other, so that at a certain stage only one is left in solution 1 . When treated in this 

 way ethylidene-lactic acid yields a dextro-rotatory solution 2 . When a current of 

 dry air is passed through sarcolactic (or ethylidene-lactic) acid heated to 150, two 

 molecules of the acid lose two molecules of water and yield a solid crystalline 

 substance known as lactide (C 3 H 4 2 ) 2 . When boiled with water this is reconverted 

 into optically inactive lactic acid, thus effecting the reconversion of the optically 

 active into the inactive form of the acid. 



The Van't Hoff-Le Bel hypothesis of what was originally called ' physical ' 

 isomerism, is based upon considerations of the spacial relationships of the con- 

 stituents of an organic substance ; hence the more recent use of the expression 

 ' stereochemical ' instead of ' physical 3 .' 



The acid reaction of dead muscle is undoubtedly due to the presence 

 of sarcolactic acid, as was first clearly shown by Liebig in 1847 4 . In 

 certain cases the reaction of muscle which is still irritable may become 

 acid and this has usually been regarded as due to the development of 

 this acid during its activity. In recent times, notwithstanding the 

 evidence of. the production of large amounts of sarcolactic acid during 

 muscular contraction (see above), the view has been put forward that 

 the acid reaction of contraction is due rather to other substances, as 

 for instance acid phosphates, than to the acid 5 . This view is by no 

 means proved and is incompatible with the preponderating evidence of 

 the researches already quoted on the relationships of this acid to mus- 

 cular activity, and of more recent observations 6 . It is possible that 

 the acid reaction of active muscle is of complex origin, being partly due 

 to lactic acid, which by acting on an alkaline phosphate may convert it 

 into an acid salt, while finally there is an excess of the lactic acid, most 

 marked in rigor. 



There is but little doubt that the glycogen normally present in 

 muscles is diminished in amount during their contracting activity, and 

 it has been frequently urged that the acid reaction of muscle is due to 

 the formation of sarcolactic acid from this glycogen. This view seems 

 to rest entirely on the fact that during activity glycogen disappears and 

 lactic acid is formed, but is devoid of convincing experimental evidence. 

 It is known that a muscle free from all glycogen can become acid during 

 activity, and bearing in mind that the acidity of active muscle is propor- 

 tional to its power of doing work, and to the work it is called upon to 



1 Gompt. Rend. T. LI. (1860), p. 153. 



2 Lewkowitsch, Ber. d. d. chem. Gesell Jahrg. 1883, S. 2720. 



3 See Miller's Elements of Chem. (Armstrong and Groves), Part III. Sec. 1, 

 (1880), p. 983, for details of the Van't Hoff-Le Bel hypothesis. 



4 That living (irritable) muscle in a state of rest is really alkaline was first 

 demonstrated by Du Bois Eeymond in 1859. Monatsber. d. Berl. Akad. 1859, S. 

 288. See his Gesammel. Abhdl. Bd. n. 1877, S. 3. 



5 Astaschewsky, Zt. f. physiol. Chem. Bd. rv. (1880), S. 397. Weyl u. Zeitler, 

 Ibid. Bd. vi. (1882), S. 557. 



6 Werther, Pfliiger's Arch. Bd. XLVI. (1890), S. 63. Of. Warren, Pfliiger's Arch. 

 Bd. xxiv. (1881), S. 391. 



F. i 



