The Respiratory Process in Muscle. 



457 



not now discuss) all these experimental results at Cambridge have been 

 gained by the use of muscle isolated from a cold-blooded animal. We have 

 already, however, sufficient assurance that in all essentials the results can be 

 taken to apply equally, mutatis mutandis, to. the case of warm-blooded 

 mammalian muscle (16). Verzar, at Cambridge (9), Winterstein and others 

 abroad, have also confirmed our results with amphibian muscle by showing 

 them again in the case of mammalian muscle. 



The considerations which have so far been brought forward seem to lead to 

 a conclusion from which there is no escape. The special processes which, when 

 they occur within a muscle fibre, culminate in a contraction, make no call 

 upon an oxygen supply ; they proceed anaerobically. The oxidations which 

 are always associated with muscular activity are separated in time from that 

 moment in which mechanical energy is liberated. They occur immediately 

 afterwards, and are concerned not with the induction of the mechanical act, 

 but with a restoration to the status quo ante. They are concerned not with 

 stimulation but with recuperation. 



Our problem, then, is to find a full description for each of these two 

 phases of change within the muscle, the anaerobic leading to contraction, the 

 oxidative resulting in recovery. 



We are concerned in this Lecture in the main with the respiratory or 

 oxidative phenomena, but in dealing with these we must, of course, have 

 regard to the muscular act as a whole. Here we would beg in advance your 

 indulgent consideration ; the main problems before us, as we have urged 

 already, lie at the centre of what knowledge we have of the processes of cell 

 fife. They lie close at every point along their borders to other great fields of 

 physiological enquiry. Their full, or, indeed, their adequate, discussion 

 should involve reference to manifold considerations in regard to the facts of 

 general metabolism, to questions of chemical energy and its transformations, 

 to the phenomena of electrophysiology, and to the intricate problems* of 

 colloidal molecular physics. In the brief scope of one lecture, we can only 

 attempt to point to the considerations which arise more immediately from 

 the experimental results we have given. 



In the first place, for the sake of greater clearness, it will be well to 

 point at once to the provisional conception we adopt of the part played in 

 muscular motion by lactic acid itself. So far from this being regarded as 

 a toxic product to tie eliminated as rapidly as possible, there is abundant 

 reason supplied by many lines of converging evidence for seeing in lactic 

 acid an essential agent in the machinery of contraction itself. The 

 development of acid, with free H-ions, in the neighbourhood of colloidal 

 fibrils gives the condition for contraction, whether by increasing the 



