292 T. Brailsford Robertson: 



excited tissue.-^) He observed that small amounts of COj 

 augment the electrical response of nerve to Stimulation and 

 that a Short tetanisation of the nerve produced a precisely 

 similar augmentation. Lee has extended this idea^) and has 

 pointed out that the action of the produots of muscular activity 

 upjon muscle is twofold; producing in moderate quantities or 

 for a short time 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. 



It appears to have escaped the notice of investigators, 

 however, that we have, in this behaviour of muscular tissue 

 a precise analogue to the behaviour of the reacting substances 

 in an autocatalysed chemical reaction, such as those described 

 above, in which one of the products of the reaction is the 

 catalyst. If we consider a muscle which is being tetanised 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 chemical changes must therefore be increasing, during 

 the period of maximal contraction and 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 

 changes is remaining 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 

 indefinitely small intervals is being stimulated at longer inter- 

 vals. During all this period the „products of fatigue", or, in 

 other words, the products of the underlying chemical reactions, 

 have been graduaUy accumulating and we have seen that as 

 the products accumulate the velocity of the reaction at first 

 increases until it reaches a maximum and then falls, in other 

 words behaves precisely in the same way as the velocity of 



1) A. D. Waller, Croonian Lecture. Phil. Trans. Roy. Soc. 

 London 188, 1, 1897. 



2) Lee, Amer. Joum. of Physiol. 18, 267, 1907. 



