134 ANNUAL REPORT SMITHSONIAN INSTITUTION, 19 34 



bination with phosphoric acid are from a chemical standpoint re- 

 markable. Very briefly stated they are these. One-half of the sugar 

 molecule is converted into a molecule of glycerin and the other half 

 into one of pyruvic acid. Now with loss of two hydrogen atoms 

 glycerin yields lactic acid, and, with a gain of the same pyruvic 

 acid, also yields lactic acid. The actual happening then is that hydro- 

 gen is transferred from the glycerin molecule while still combined 

 with phosphoric acid to the pyruvic acid molecule with the result 

 that two molecules of lactic acid are formed. The lactic acid is then, 

 during a cj^cle of change which I must not stop to discuss, oxidized 

 to yield the energy required by the muscle. 



But the energy from this oxidation is by no means directly avail- 

 able for the mechanical act of contraction. The oxidation occurs 

 indeed after and not before or during a contraction. The energy it 

 liberates secured however the endothemic resynthesis of a substance, 

 creatin phosphate, of which the breakdown at an earlier stage in 

 the sequence of events is the more immediate source of energy for 

 contraction. Even more complicated are these chemical relations, 

 for it would seem that in the transference of energy from its source 

 in the oxidation of carbohydrate to the system which synthesizes 

 creatin phosphate, yet another reaction intervenes, namely, the alter- 

 nating breakdown and resynthesis of the substance adenyl pyrophos- 

 phate. The sequence of these chemical reactions in muscle has been 

 followed and their relation in time to the phases of contraction and 

 relaxation is established. The means by which energy is transferred 

 from one reacting system to another has till lately been obscure, 

 but current work is throwing light upon this interesting question, 

 and it is just beginning (though only beginning) to show how at the 

 final stage the energy of the reactions is converted into the mechan- 

 ical response. In parenthesis it may be noted as an illustration of 

 the unity of life that the processes which occur in the living yeast 

 cell in its dealings with sugars are closely similar to those which 

 proceed in living muscle. In the earlier stages they are identical 

 and we now know where they part company. You will, I think, be 

 astonished at the complexity of the events which underlie the activity 

 of a muscle, but you must remember that it is a highly specialized 

 machine. A more direct burning of the fuel could not fit into its 

 complex organization. I am more particularly concerned to feel 

 that my brief summary of the facts will make you realize how much 

 more definite, how much more truly chemical, is our present knowl- 

 edge than that available when Michael Foster wrote: Ability to 

 recognize the progress of such definite ordered chemical reactions in 

 relation to various aspects of living activity characterizes the cur- 

 rent position in biochemistry. I have chosen the case of muscle, 

 and it must serve as my only example, but many such related and 



