1 86 HUMAN PHYSIOLOGY 



muscle albumin. The remainder is chiefly composed of a 

 proteid, called myogen. 



The muscle also contains an undissolved proteid of unknown 

 nature, collagen, and the nuclein-like phosphocarnic acid which, 

 by splitting up, yields phosphoric acid, a sugar-like product, lactic 

 acid, and carnic acid, a substance belonging to the peptones. 



In addition to the above-named proteids, the muscles contain 

 a pigment, myohaematin, which is identical with the haemoglobin 

 of the blood; but it is not derived from haemoglobin, for animals 

 without blood also have this pigment in their muscles. 



2. Carbohydrates, chiefly glycogen, stored up between 

 the muscle fibrils ; grape-sugar in small and varying amounts ; 

 inosit. 



3. Fats, chiefly deposited in the intramuscular connective 

 tissue. The amount varies with nutrition. 



4. End-products of metaboHsm, chiefly keratin and 

 xanthin bases; also sarcolactic acid. 



5. Salts, especially potassium phosphate. 



Muscles contain carbon dioxide, but no free oxygen can 

 be obtained from them. 



(b) Chemical processes in tJie resting muscle. The 

 physiological combustion in the resting muscle manifests 

 itself by the consumption of oxygen and the production of 

 carbon dioxide. This is evident from the fact that arterial 

 blood is changed to venous blood in the muscles. 



2. Mechanical properties of a resting muscle. The 

 muscle is elastic and, in the longitudinal direction of its 

 fibres, extensible. During this extension, the length of the 

 muscle increases, its thickness decreases ; its volume under- 

 goes no change. 



The elongation during extension is not proportional to the 

 weight which causes the extension, for the extension pro- 

 duced by one and the same weight is the less, the more the 

 muscle is already stretched. Hence the curve of extension, 

 i.e. the curve whose abscissa represents the weight and 

 whose ordinate represents the length of the muscle, is not a 

 straight line, but a hyperbola (see page 192). 



