266 THE ANIMAL. XII. 



Fat is also present, together with lecithin. 



The gases present in muscle consist mainly of carbon 

 dioxide and traces of nitrogen. 



Of the mineral constituents potassium and phosphoric acid 

 are the chief; sodium, magnesium, calcium, chlorine, and iron 

 are also present. Sulphates are found in the ash, but 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 nutri- 

 tive value rather than the true composition. 



The following analyses are quoted by Hammarsten : 



Muscle from p . , , Cold-blooded 



w mammalians. animals. 



Solids ... 21-7 to 25-5 22-7 to 28-2 20-0 



Water ... 74-5 to 78'3 71-7 to 77-3 8OO 



Myosin ... 3-5 to 10-6 2-98 to 11-1 2-97 to 8-7 



Stroma ... 7'8 to 16-1 8-8 to 18-4 7-0 to 12-1 



Alkali-albuminate 2-9 to 3-0 



Creatin ... -2 3-4 2-3 



Xanthin bodies... -04 to -07 -07 to -13 



Inosit ... -003 



Glycogen ... -4 to -5 -3 to -5 



Lactic acid ... -04 to -07 



and a very variable amount of fat. 



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 tem- 

 perature. 



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 



