MUSCLE 255 



amount of oxygen used in muscles at rest and in action is 

 ascertained by determining (1) the decrease in the amount of 

 oxygen in the blood leaving the muscles (p. 498) ; (2) the 

 amount of blood flowing through the muscles per unit of 

 time (p. 473); and (3) the weight of the muscle. This 

 allows the coefiicient to be stated in terms of c.cm, of oxygen 

 per grm. of muscle per minute. In the skeletal muscles of 

 mammals the following variations have been found according 



to the condition of activity : oxygen per minute per 



Nerve cut : Tone absent . 

 Tone existing in rest 

 Gentle Contraction , 

 Active Contraction 



grm. of muscle in c.cm. 



0-003 

 0-006 

 0-020 

 0-080 



With active contraction the consumj^tion of oxygen may 

 be increased more than twenty-fold. 



Similar results are obtained when the influence of 

 muscular work upon the oxygen consumption of the body 

 as a whole is studied (p. 26 6 j. 



Is this increased oxidation in contraction accompanied 

 by any change in the composition of the muscle ? So long 

 as the blood stream is intact it is probable that any change 

 which may occur is at once made good. But if muscle 

 deprived of its blood supply is investigated it is unsafe to 

 conclude that a change in composition is the result of 

 contraction and is not due to the decreased supply of blood. 

 It has been shown that when muscle contracts without a 

 supply of oxygen, sarcolactic acid accumulates ; but that 

 when it contracts in oxygen, this is oxidised to carbon dioxide 

 (p. 249). In contraction the supply of glycogen in muscle 

 is decreased, and after fasting and strychnine convulsions, it 

 may practically disappear. 



(2) Material Oxidised by Muscle. — The study of the co- 

 efiicient of oxidation of muscle leads to the consideration of 

 what is oxidised to yield the energy. 



It has been found that only the three great constituents 

 of the body and of the food — the proteins, carbohydrates, 

 and/aZ'.s — are freely oxidised to yield energy in the body, 

 although some other substances, e.g. alcohol, are capable of 

 a limited oxidation. 



