25 6 SCIENCE PROGRESS 



Evidence of another kind in favour of a glycolytic enzyme 

 has been obtained by Weinland. 1 He found that not only did 

 intestinal worms (Ascaris lumbricoides) , when kept in the com- 

 plete absence of oxygen, form C0 2 and valerianic acid at the 

 expense of their store of glycogen, but that the expressed juice 

 of the worms effected a similar decomposition on glycogen and 



glucose. 



It will be gathered from this brief statement of the evidence 

 that at present we cannot definitely assume the existence of a 

 zymase in animal tissues, though we are probably justified in 

 accepting the existence of other glycolytic enzymes. It is by no 

 means improbable that zymases are present, but they may be 

 even more unstable than the zymase of vegetable tissues, and so 

 require special methods for their demonstration. 



In addition to the hydrolytic decomposition of tissue con- 

 stituents by enzyme action, it seems probable that in muscle, if 

 not in other tissues, some of them can undergo sudden disin- 

 tegration by intramolecular changes induced by an external 

 stimulus. By means of a very delicate thermopile V. T. Hill 2 

 has shown that if a frog's sartorius muscle be kept in an atmo- 

 sphere of nitrogen, the heat produced on excitation occurs only 

 during, or shortly after, the mechanical response, and not during 

 long periods after it. There are good grounds for thinking that 

 the evolution of heat and mechanical energy are due to the 

 sudden decomposition of an unstable chemical substance which 

 forms lactic acid as its chief decomposition product. From his 

 thermo-electric data Hill 3 calculates that this lactic-acid pre- 

 cursor possesses about 10 per cent, greater total energy than the 

 lactic acid itself. Hence it cannot be glucose, as this possesses 

 at most only 3 per cent, more energy than lactic acid. The pre- 

 cursor is not to be confounded with Hermann's " inogen," for 

 this labile muscle molecule was supposed to break down into 

 lactic acid, C0 2 and water, or to undergo combustion at the 

 expense of intramolecular oxygen, which had previously been 

 taken up and stored within it. So far from accepting this 

 hypothesis Fletcher considers that there is no good evidence 

 that the lactic precursor forms any C0 2 whatever at the moment 



1 Weinland, Zeit.f. Biol. 42, p. 55, 1 901 ; 43, p. 86, 1902. 

 J V. T. YixWJoum. Physiol. 42, p. 29, 191 1 ; 46, p. 28, 1913. 

 1 V. T. Hill, ibid. 44, p. 466, 1912. 



