272 



MUSCLE 



The gases present in muscle consist mainly of carbon dioxide, with 

 traces of nitrogen. 



Of the mineral constituents, potassium and phosphoric acid are the 

 chief; sodium, magnesium, calcium, chlorine and iron are also pre- 

 sent. Sulphates are found in the ash, hut probably are derived from 

 the sulphur of the proteids. 



Detailed analyses of muscle are rarely made, most published 

 analyses having for their object the determination of the nutritive value 

 rather than the true composition. 



The following analyses are quoted by Hammarsten : 



Living muscle has an alkaline reaction, but after death a change 

 occurs, and it acquires an acid reaction, due probably to the formation 

 of sarcolactic acid. 



When muscle contracts, oxidation goes on at an accelerated rate 

 and more carbon dioxide is produced and carried away in the blood 

 which bathes the muscle. The consequent increased production of 

 heat is consumed, partly in doing the mechanical work performed by 

 the muscle and partly in raising the temperature. 



The glycogen and sugar are the chief sources from which this 

 energy is derived. Fat may be consumed if the carbohydrates are in 

 insufficient quantity ; but although early experimenters concluded that 

 muscular exertion increased the quantity of nitrogenous waste from 

 the body, more recent researches tend to show that this is not the case. 

 The nitrogenous waste is chiefly excreted in the form of urea in the 

 urine and sweat. 



Connective Tissue. This material, which constitutes the main 

 ingredient in the tendons, ligaments, cartilages, skin, etc., of the animal 

 body, consists essentially of gelatine-yielding substances, of which the 

 following are the chief : 



(1) Elastin, an insoluble substance containing little or no sulphur. 

 Its composition, according to analyses quoted by Hammarsten, is 

 about 



