GENERAL MUSCLE PHYSIOLOGY 187 



2. THE STIMULATED OR ACTIVE MUSCLE 



i. Chemical processes in the active muscle. In the 



active muscle the processes of combustion are enormously 

 increased. During muscular activity the consumption of 

 oxygen and the formation of carbon dioxide maybe increased 

 to four or five times that during rest. During this activity 

 more carbohydrates or fats are used, while the consumption 

 of proteid remains the same, if sufficient fat and carbohy- 

 drate are present. But if these are not present in sufficient 

 quantities, the muscular activity takes place at the expense 

 of proteid. This is evident from the metabolism of the body 

 during rest and work. The taking up of oxygen and the 

 giving off of carbon dioxide are always enormously increased 

 by muscular activity, but the nitrogenous excretions are only 

 increased when the food does not contain sufficient non- 

 nitrogenous substances to supply the energy for the work, 

 e.g. during purely proteid diet. 



The respiratory quotient is not changed by muscular 

 activity, if the work is not extreme; but if the work is 

 fatiguing, it is increased. 



The amount of glycogen in the muscles and in the liver 

 is decreased by work. Body fat may also be lost by work. 



The active muscle has an acid reaction. Sarcolactic acid 

 of the muscle is increased by activity. 



Although no trace of free oxygen is present in the muscles of a 

 frog, still an excised frog-muscle placed in an atmosphere free of 

 oxygen can do work. They therefore contain oxygen stored up 

 in the form of chemical compounds which can be used when 

 necessary. 



Muscles of warm-blooded animals contain, at best, only a small 

 supply of stored-up oxygen, for they lose their irritability soon 

 after the supply of arterial blood is cut oft. 



The amount of substances capable of extraction with water is 

 decreased by activity, while those extracted by alcohol are 

 increased. It is said that the amount of phosphocarnic acid 

 [phosphorfleischsaure] in the muscles is decreased by activity. 



