CHEMICAL ASPECTS OF LIFE HOPKINS 133 



Research, however, during the present century, much of which has 

 been done since the association last met in Leicester, has yielded 

 knowledge to justify the optimism of the few who started to work in 

 those days. Were there time, I might illustrate this by abundant 

 examples; but I think a single illustration will suffice to demon- 

 strate how progress during recent years has changed the outlook for 

 biochemistry. I will ask you to note the language used 30 years ago 

 to describe the chemical events in active muscle and compare it with 

 that used now. In 1895 Michael Foster, a physiologist of deep vision, 

 dealing with the respiration of tissues, and in particular with the 

 degree to which the activity of muscle depends on its contemporary 

 oxygen supply, expounded the current view which may be thus 

 briefly summarized. The oxygen which enters the muscle from the 

 blood is not involved in immediate oxidations, but is built up into the 

 substance of the muscle. It disappears into some protoplasmic com- 

 plex on which its presence confers instability. This complex, 

 like all living substance, is to be regarded as incessantly undergoing 

 changes of a double kind, those of building up and those of breaking 

 down. With activity the latter predominates, and in the case of 

 muscle the complex in question explodes, as it were, to yield the en- 

 ergy for contraction. " We cannot yet trace ", Foster comments, 

 " the steps taken by the oxygen from the moment it slips from the 

 blood into the muscle substance to the moment when it issues united 

 with carbon as carbonic acid. The whole mystery of life lies hidden 

 in that process, and for the present we must be content with simply 

 knowing the beginning and the end." What we feel entitled to say 

 today concerning the respiration of muscle and of the events asso- 

 ciated with its activity requires, as I have suggested, a different 

 language, and for those not interested in technical chemical aspects 

 the very change of language may yet be significant. The conception 

 of continuous building up and continuous breakdown of the muscle 

 substance as a whole, has but a small element of truth. The colloidal 

 muscle structure is, so to speak, an apparatus, relatively stable even 

 as a whole when metabolism is normal, and in essential parts very 

 stable. The chemical reactions which occur in that apparatus have 

 been followed with a completeness which is, I think, striking. It is 

 carbohydrate stores distinct from the apparatus (and in certain 

 circumstances also fat stores) which undergo steady oxidation and 

 are the ultimate sources of energy for muscular work. Essential 

 among successive stages in the chemical breakdown of carbohydrate 

 which necessarily precede oxidation is the intermediate combination 

 of a sugar (a hexose) with phosphoric acid to form an ester. This 

 happening is indispensable for the progress of the next stage, namely 

 the production of lactic acid from the sugar, which is an anaerobic 

 process. The precise happenings to the hexose sugar while in com- 



