MUSCLE 



207 



II. Chemistry of Muscle. 



Like all other living tissues, muscle is largely composed 

 of water. It contains about 75 per cent. The 25 per cent, 

 of solid constituents is made up of a small quantity, about 

 2 per cent, of ash, and 22 per cent, of organic sub- 

 stances. 



The following table gives an idea of the average com- 

 position of mammalian muscle freed from visible fat : — 



1. Proteins. — Of the organic constituents, by far the 

 greater part is made up of Proteins. 



They may be extracted either by — 



A. Cooling the muscle at once to near the freezing-point 

 and expressing the juice in a press. 



When the temperature is raised the fluid tends to clot, 

 becoming a gel on account of some change in the colloidal 

 complex. The clot is myosin, and it is of the nature of a 

 globulin. 



B. Rubbing the muscle in a mortar with NaCl, and 

 then diluting so as to make a 5 per cent, solution of 

 the salt. By this method the proteins may be divided 

 into — 



(1) Those soluble in neutral salt solutions. 



(2) Those insoluble in them. 



(1) These 



belong 



to the class of 



globulins. 



They 



are 



(a) Myosinogen, which constitutes about 75 per cent, of 



