172 



THE MUSCLE CELLS 



111 the recovery stage the anaerobic processes are followed by 

 cht^iiieal changes involving the use of oxygen. Practically all the 

 simpler quantitative experiments have been carried out iso- 

 metrically, as that type of contraction is free from the complication 

 of the various extra factors involved in an isotonic contraction. 

 In the absence of oxygen a muscle produces heat equivalent to 

 3-8 X 10'^ ergs for every gram weight of muscle. This amount of 

 heat (0-9 calorie) is divisible over the three anaerobic stages as 

 follows : 



1. Initiation of contraction 



2. Maintenance of contraction 



3. Relaxation . 



12-5 X 10^ ergs. 

 6-2 X 10*5 ergs. 



. n-7 X 10*5 ergs. 



leaving 7-6 X 10^ ergs as equivalent to the heat evolved during 

 (4) imperfect anaerobic recovery. 



If the contracting muscle has adequate supplies of oxygen, the 

 heat evolved during the last stage wall be spread over a considerable 

 period of time and will amount to about six times the anaerobic 

 recovery heat = 45-6 X \Q^ ergs. The earlier stages will have the 

 same heat production under both anaerobic and aerobic conditions. 

 During this process of restitution a large amount of lactic acid 

 liberated during the earlier phases disappears (Table XXVII.). 

 Some of it is rebuilt into glycogen absorbing a definite amount of 

 energy which may be produced by the oxidation of other lactic 

 acid molecules. For every gram of lactic acid formed in the earlier 

 stages in the absence of oxygen, about 0-81 gram is restored to 

 muscle to rebuild glycogen, while the remainder, 0-19 gram, is 



oxidised to COg and H.^O. That is, 0-81 gram lactic acid > 0-81 



gram (approx.) of glycogen with absorption of 1008 X 10^ ergs 



= 240 cals. 0-19 gram lactic acid > COg + H2O + 2873 X 10^ 



ergs = 684 cals. 



TABLE XXVII 



Percentage of Glycogen and Lactic Acid in Muscle 



Thi.s table of averages, taken from the experiments of Olmstead and 

 Coulthard (Anier. Journal of Physiology, LXXXIV., 1928), shows clearly that 

 what is lost in glycogen content during activity is quantitatively gained in 

 lactic acid content. 



