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



produced by muscle contraction or upon dying is oxidisable, or in some way 

 removable by oxygen, with an accompanying production of carbon dioxide. 

 The next step was to obtain direct evidence of the changes undergone by 

 lactic acid in muscle. Lactic acid outside muscle, in the circulation for 

 instance, is not directly oxidisable at physiological temperatures. 



Lactic Acid in Muscle. 



It is a remarkable fact that up to less than ten years ago we had little or 

 no knowledge of the most elementary relations of this acid to the physiology 

 of muscle. Production of free acid appears to be an almost universal sign of 

 the activity of any living cell, and a sign also of the processes leading to 

 death ; but even in the conspicuous case of muscle nothing was known 

 certainly with regard to the conditions of lactic acid production, save the fact 

 of its happening. This is another striking instance of the slenderness of the 

 foundation upon which the inogen hypothesis had been erected, and with it, 

 as we have seen, almost the whole structure of prevalent ideas with regard to 

 the general nature of the processes of metabolism. 



The inherent difficulty besetting the chemical examination of muscle lies, 

 of course, in the fact that the necessary processes for extraction of the 

 constituents cause in the moment of their application profound chemical 

 change. It will not be appropriate here to explain in detail the chief 

 fallacies underlying the methods which had formerly been used. It may be 

 said, however, that up to a few years ago there was hardly any single 

 statement made with regard to the conditions of lactic acid appearance in 

 muscle which was not both supported and contradicted by rival sets of 

 observers respectively. 



In our own work (5), of which we propose to give very shortly the chief 

 results, we found that the disturbing influences introduced by the mechanical 

 and chemical operations necessary to the process of investigation, could be 

 reduced to a minimum if throughout the whole of their performance the muscle 

 was maintained at a temperature close to the freezing point. Completely 

 resting muscle examined in this way in the cold, when the cold is maintained 

 until the extracting processes are complete and the muscle killed, gives only 

 the smallest traces of lactic acid, and these traces must be attributed to the 

 unavoidable minimum- of manipulation before the low temperature is 

 reached. Eesting muscle, that is to say, may be regarded as muscle 

 contaiuing at most only traces of free lactic acid. 



In order to determine the lactic acid production associated with any 

 particular muscular condition, whether of fatigue or of spontaneous resting 

 change, the* processes of examination were carried out again only when the 



