DR. PAVY AND DIABETES 37 



in the evolution of carbon dioxide at all proportionate to the 

 work done. No acceleration in its evolution is observed 

 beyond what is accounted for on the lines just mentioned. 

 But lactic acid does increase as a result of the contractions 

 and increases at a rate proportionate to the work done. Its 

 production is undoubtedly due to the processes which yield 

 energy to the contracting muscle. Now if an excised muscle 

 which has accumulated lactic acid as a result of oxygen defi- 

 ciency be given a supply of oxygen, its lactic acid proceeds to 

 disappear and if, as I have already stated, the oxygen supply 

 be adequate from the first the acid never accumulates, there 

 being proportionality between its formation and removal. 

 Upon such facts as these is based what I believe to be the 

 sound view that the energy of muscular activity is derived 

 from a non-oxidative molecular breakdown of which lactic acid 

 is a product. Upon this breakdown follows an oxidative re- 

 moval of the products which normally keeps pace with their 

 production. A careful study of the thermal relations of the 

 phenomena has largely justified this view. 



Now if we were quite sure that the lactic acid which 

 appears in muscle were derived from sugar directly, we should 

 have clear evidence for the occurrence of that change in the 

 sugar molecule, preceding oxidation, which we were seeking in 

 order to explain the existence of a normal oxidative power in the 

 diabetic organisation side by side with its inability to oxidise 

 sugar. There is every probability that the lactic acid is derived 

 in some way from carbohydrate but the facts prevent our 

 taking a quite simple view of the relation. The derivation of 

 lactic acid from dextrose involves only a rearrangement of 

 atoms in the sugar molecule — C 6 H 12 6 = 2C 3 H 6 3 — and the 

 change leads to a very small liberation of energy, some 3 per 

 cent, only of the total energy in the sugar being involved. 

 A calculation of the actual quantities concerned, however, 

 has led to the belief that the energy so liberated is, as a 

 matter of fact, sufficient to supply the contracting muscle with 

 its requirements ; but a very recent investigation into the 

 heat production of muscle during survival life points to the 

 fact that the actual precursor of the lactic acid must possess 

 at least 10 per cent, more energy than the acid itself 1 ; dextrose, 

 as we have seen, contains only some 3 per cent. more. 



1 A. V. Hill : private communication. 



