CONVERSION OF CHEMICAL INTO MECHANICAL ENERGY 439 



stimulation and that a short tetanization of the nerve produced a pre- 

 cisely similar augmentation. Lee has extended this idea to muscular 

 tissues and he has pointed out that the action of the products of 

 muscular activity upon the performance of muscular work is two-fold 

 producing in moderate quantities or for a short time a marked increase 

 in the irritability and working-power of the muscle, while in larger 

 quantities or after a longer period of action they produce a marked 

 depression or "Fatigue*' of the muscle, ending by totally preventing the 

 further release of muscular energy. The nature of the products which 

 bring about these results has been established by Lee, who has found 

 that perfusion of a muscle with a dilute solution of Lactic Acid or an 

 acid phosphate increases its irritability and power to do work, while 

 more concentrated solutions of the same substances diminish and 

 finally abolish its irritability and contractility. Both of these sub- 

 stances are known, by direct estimation, to accumulate in a muscle 

 which is doing work. 



If we consider a muscle which is being tetanized by rapidly repeated 

 stimuli, it is evident that the rate at which the muscle is doing work 

 may be regarded as an expression of the rate at which the underlying 

 chemical changes are taking place. During the initial or rising part of 

 the curve of tetanus which is nearly always to be observed, the velocity 

 of the underlying chemical changes must be increasing. During the 

 period of maximal contraction while the recording-lever remains at a 

 constant level it is evident that the rate of doing work and therefore 

 the velocity of the underlying chemical change are practically constant, 

 during the third, or descending part of the curve the velocity of the 

 chemical changes is evidently decreasing. Similar considerations 

 apply, of course, when the muscle, instead of being stimulated at 

 extremely small intervals, is being stimulated at longer intervals. 



The chemical changes which underlie and determine muscular con- 

 traction are of such a character, therefore, that one or more of the 

 products which result, first accelerate and later retard the process. We 

 are familiar with many chemical reactions of this type; they are reactions 

 in which one of the products acts as a catalyzer to the process and are 

 therefore designated Autocatalyzed Reactions. Thus in the hydrolysis 

 of Cane-sugar by neutral boiling water small quantities of mucic acid 

 are developed which greatly accelerate the inversion. The hydrolysis 

 of Methyl Acetate by water results in the liberation of acetic acid which 

 very greatly accelerates the hydrolysis. The hydrolysis of the Ricino- 

 leic Acid in pulverized castor-oil beans proceeds at first very slowly, 

 and then with great rapidity, the acid which is first liberated enhancing 

 the activity of the lipase in the macerated tissues. Instances of auto- 

 catalytic oxidations are afforded by the spontaneous oxidation of many 

 Metals and organic compounds in the presence of oxygen at atmos- 

 pheric temperature and pressure. It has long been observed that in 

 the spontaneous oxidation of these substances they acquire the power 

 of inducing oxidations in other substances which are not spontaneously 



