276 MUSCLES 



that of the ordinary striated tissue and greater than that 

 of the unstriated. It is also remarkable for the rhythmic 

 character of its contractions. 



Composition of Muscle. 



Applying the common food tests to muscles we find 

 them to be composed mainly of proteid and water with a 

 small quantity of the salts, carbohydrates, fats, nitro- 

 genous wastes, and enzymes. 



Muscle proteids. — There are two forms of muscle proteid: one 

 known as myosin, the other as myogen. The myogen is most 

 abundant in living muscle, for it is present to three or four times 

 the bulk of the other. Both are coagulated by heat, but the 

 myogen requires a higher temperature (131°-149° F.) than the 

 other (113°-122° F.). Both are similar to the fibrinogen of the 

 blood, for when they are allowed to stand at ordinary tempera- 

 tures they are capable of forming a clot, and of assuming an in- 

 soluble form called myogen-fibrin or myosin-fibrin, just as fibrin- 

 ogen is transformed into fibrin by the clotting of blood. Dead 

 muscle then consists mainly of clotted myosin and myogen, or 

 myosin-fibrin and myogen-fibrin. This clotting is supposed to 

 explain what is known as " rigor mortis " or the stiffening of the 

 muscles after death. 



Muscle carbohydrates. — The carbohydrates present in muscle 

 are sugar and glycogen. It is supposed that muscle has the power 

 to convert sugar into glycogen and glycogen into sugar as needed. 

 In action the glycogen is first transformed into sugar and then 

 consumed in the production of the energy. We can assume then 

 that the glycogen in the muscle represents sugar brought to it 

 by the blood, converted by it and stored in the form of glycogen 

 until the muscle needs it. It is a reserve supply of fuel in the 

 muscle. 



Muscle Enzymes. — Muscles contain a number of enzymes. 

 The following have been identified : A proteolytic enzyme capable 



