454 MANUAL OF PHYSIOLOGY. 



The chemical changes which are commonly said to take place 

 in muscle during its contraction are : 



1. The contractile substance, which is normally neutral or 

 faintly alkaline, becomes acid in reaction, owing to the formation 

 of sarcolactic acid. 



2. More oxygen is taken up from the blood than in the muscle 

 at rest. This using up of oxygen occurs also in the isolated 

 muscle, and its amount appears to be independent of the blood 

 supply. 



3. The extractives soluble in water decrease, those soluble in 

 alcohol increase. 



4. A greater amount of CO 2 is given off, both in the isolated 

 muscle as well as in the muscles in the body, and the change in 

 the quantity of CO 2 has no exact relation to that of the oxygen 

 used. 



5. A diminution is said to occur in the contained glycogen,and 

 certainly prolonged inactivity causes an increase in the amount 

 of glycogeu. 



6. A peculiar muscle-sugar makes its appearance. 



Change in Elasticity. The elasticity of a muscle during its 

 state of contraction is less than when it is in the passive state. 

 That is to say, that a given weight will extend the same muscle 

 more if attached to it while contracted (as in tetanus) than when 

 it is relaxed. The contracted muscle is then more extensible. 

 If, then, a weight which is just over the maximum load the mus- 

 cle can lift, be hung from it and the muscle then stimulated, it 

 should become extended, because the change to the active state 

 lessens its elastic power, while it cannot contract, being over- 

 weighted. 



Electrical Changes. If a muscle, in connection with a galvano- 

 meter, so as to show the natural current, be stimulated by means 

 of the nerves, a marked change occurs in the current. The gal- 

 vauometric needle swings towards zero, showing that the current 

 is weakened or destroyed. This is called the negative variation 

 of the muscle current which initiates the change to the active 

 condition. When the muscle receives but a momentary stimulus 

 so as only to give a single contraction, this negative variation 



