448 Dr. W. M. Fletcher and Prof. F. G. Hopkins. 



On contraction in oxygen, and now even on slight contraction, it yielded the 

 increase of carbon dioxide expected by the text-books to be shown in air [(3) 



and tig. 2.] 



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Fig. 2. — Course of survival discharge of carbon dioxide from two " crossed ' : pairs of 

 gastrocneruii. Contraction periods are shaded. Temp. 17° C. (In the first contrac- 

 tion period slow rhythmic stimuli were given and fatigue was not shown ; in the 

 second period, rapid stimuli we're given and the muscles were fatigued to a stand- 

 still.) For details see the 'Journal of Physiology,' vol. 28, p. 474 (1902). 



It may be said in passing that these results accorded with many observations 

 made previously upon the whole animal in which conditions of imperfect 

 oxygen supply had given apparent incompletion of oxidative processes, and 

 explained many earlier discordant observations made when blood was circulated 

 through muscle. 



It became clear then that the contemporary and immediate supply of 

 oxygen did affect the products due to contraction, and the inogen theory, 

 postulating a previous inclusion of oxygen within the muscle elements, was 

 evidently inadequate. 



We now come to the second of the two pillars of the inogen hypothesis — 

 the effects of heat upon muscle and the supposed " fixation " of inogen by rapid 

 scalding. The close historical dependence of the hypothesis upon the 

 experimental results of heating has not, we think, been sufficiently recognised. 



Du Bois Eeymond had made the observation that a muscle if slowly killed 

 by heat became markedly acid, but not if it was rapidly killed by scalding. 

 Hermann, in his view of inogen, assumed that lactic acid and carbon dioxide 

 found in it their common and simultaneous source of origin, and, probably 

 biassed by this, he claimed to show experimentally that scalded muscle 

 yielded not only no lactic acid, but also no carbon dioxide ; but in fact, 

 though this simply tested phenomenon became the commonplace of the text- 



