340 Food as a Motive Power. [July, 



as that of the so-called respiratory elements of the food ; and I find 

 it impossible to dissent from this view. Kanke, in his splendid 

 essay,* has indeed made use of these facts in support of the theory 

 of Liebig, but valuable as his researches are, they can hardly be 

 said to have made out his case. He proved that some of the pro- 

 ducts of the decomposition of muscle, and particularly lactic acid, 

 had the power of hindering or even of arresting muscular movement. 

 He found that the feeling of fatigue in an overworked muscle was 

 mainly due to the accumulation of lactic acid in it ; that it could be 

 removed by washing out the lactic acid with water, and induced in 

 a muscle which had been long at rest by the injection into it of a 

 solution of lactic acid, or even of an aqueous decoction of a fatigued 

 muscle ! From these and numberless other experiments he argued 

 that the amount of work done by an animal was nearly constant, 

 unusual muscular exertion being always followed by a corresponding 

 period of quiescence, which lasted until the products of disintegra- 

 tion were removed from the muscles, or neutralized. But his expe- 

 riments, although extremely ingenious, were necessarily only of a 

 qualitative kind, and cannot therefore be put in opposition to the 

 direct quantitative proofs alleged upon the other side. 



But there is a third view of this great question which was 

 clearly propounded by Mayer, but which seems to have been 

 unaccountably neglected by later physiologists. It appears to me 

 to afford a means of reconciling many of the difficulties which beset 

 the subject. It is founded upon a consideration of the function 

 which the blood fulfils in the matter. When blood traverses the 

 capillaries of a muscle, it becomes darkened in colour. A portion of 

 its colouring matter is reduced to the purple state, and at the same 

 time some of the corpuscles disappear. During muscular contrac- 

 tion these changes are intensified, and the loosely combined oxygen 

 of the colouring matter may even, as Ludwig and Sczelkow have 

 found, be reduced to one-third of the average amount present during 

 rest. Hence, muscular contraction is attended with a more rapid 

 consumption of the oxygen of the corpuscle. According to the 

 current theories we are therefore compelled to suppose that on the 

 stimulus of the motor nerve, oxygen leaves its combination in the 

 corpuscle, passes through, without combining with the easily oxidiz- 

 ible constituents of the liquor sanguinis, traverses the thin walls of 

 the capillary in company with the outgoing nutritive fluid, and only 

 exerts its force and produces oxidation when it is in contact with 

 some comparatively distant muscle fibre. That this is the view 

 usually taken by physiologists is shown by an incidental remark 

 made by Dr. Bence Jones, in his address as President of the 

 chemical section of the British Association at the last meeting. 



* Tetanus — Eine Physiologische Studie. Leipzig, 1865. 



