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



undergoing chemical modification, cany changes of potential as a result of 

 changes in its physical configuration, it becomes easier for us to realise that the 

 food-stuffs, or at least that sugar, may be the direct source of the contractile 

 energy. Placed in the right locality within the muscle, sugar, by a non- 

 oxidative yield of acid at the right moment, and by a subsequent oxidation 

 of this at another right moment, can yield its total energy in a manner 

 exactly suited to serve the peculiar machinery in which, so to speak, it finds 

 itself. 



The actual chemical events which underlie the obvious manifestations of 

 change in muscle — the contraction, the exhibition of fatigue, the recovery — 

 we might then regard as relatively simple. We find similar indications in 

 all progressive departments of biochemistry. The chemical events are not 

 in themselves necessarily complex or obscure ; the complexity is found in the 

 conditions under which they occur. The difficulties of the biological enquirer 

 arise from the fact that he has, for the most part, to accept these conditions 

 as given. It is usually open to the physicist or pure chemist to control and 

 simplify the conditions of his experimental work, or wisely to avoid regions 

 of complexity until collateral progress has made them simple. In biology 

 the complexities of the conditions are in the essence of the phenomena, and 

 the experimentalist, when he tries to simplify them, is even viewed with 

 suspicion. Thus even the operation of excising a muscle before studying its 

 chemistry has been regarded with some prejudice, though in this case we 

 think we may fairly claim that the progress made in the long series of 

 enquiries' we have discussed, has illustrated the fact that the biologist is after 

 all not wholly shackled by the necessity of putting all his questions to the 

 intact animal. 



The description of muscle activity we have attempted to give remains, it 

 is true, imperfect ; indeed, we hardly yet have knowledge enough to guess 

 how imperfect it is. But recent studies have had at least the result of 

 confirming our own faith in the powers of experiment to bring improvement 

 of knowledge, and we venture to believe that they have already indicated 

 hopeful lines for further experimental work. 



The following publications, to which reference has been made in the 

 Lecture, are based upon researches which have been carried out in the 

 Physiological Laboratory at Cambridge : — 



(1) W. M. Fletcher, "The Survival Kespiration of Muscle," ' Journal of Physiology,' 

 vol. 23, p. 10 (1898). 



(2) W. M. Fletcher, " The Influence of Oxygen upon the Survival Kespiration of 

 Muscle," ibid., vol. 28, p. 354 (1902). 



