MUSCLE. 85 



What is the chemical composition of muscle ? 



Water is a chief ingredient, and myosin the characteristic one. 

 Salts are found, chiefly of potassium. Various proteids, such as 

 gelatin, elastic material, and albumins, are found, together with 

 fats and extractives. The extractives are mostly complex organic 

 compounds : among them may be mentioned kreatin, lactic acid, 

 and sugar. Urea is not found, except in minute quantities, though 

 it is regarded as originating from the waste products of muscular 

 action. The following table formulates the proportion of these con- 

 stituents : 



Water 745 



Solids : 



Myosin and insoluble proteids 155 



Soluble proteids 20 



Gelatin 21 



Fats 23 



Organic and inorganic salts 36 



1000 

 What is the reaction of live muscle ? 



Alkaline, due to the presence of potassium phosphate. 



What is the function of the muscles ? 



They contract and cause motion in the parts to which they are 

 attached. During life the muscles are always tense, and this con- 

 dition favors a more powerful action when the muscles contract in 

 response to stimuli. 



How do the muscles affect the blood passing through them ? 



They abstract much of the oxygen and give off large amounts 

 of carbonic acid, so that blood after circulating through the mus- 

 cles, even when they are at rest, becomes very dark. It is probable 

 that an abundance of oxygen is especially essential to the healthy 

 condition of the muscles, and it is found that in an atmosphere of 

 oxygen muscles retain their power of contraction longer than in 

 one of hydrogen or carbonic acid. 



What peculiar electrical condition is noticed in living muscle ? 



When a living muscle is tested by means of the galvanometer 

 after removal from the body, it is found to develop certain electri- 

 cal currents known as muscle-currents or currents of rest. They are 



