582 A MANUAL OF PHYSIOLOGY 



Water 75 per cent. 



Proteids 20 



Fats 2 



Nitrogenous fggfr 

 metaboHtes. Igj^thb, 



Carbohydrate, {g&cdc acid 



Inosit 



Salts, chiefly carbonate and phosphate of potassium, less than 

 I per cent. 



There is more water in the muscles of young than of old animals 

 (v. Bibra), and more in tetanized than in rested muscle (Ranke). 

 The fats probably belong to a small extent to the actual muscle- 

 fibres. For even when the visible fat is separated with the utmost 

 care, nearly i per cent, of fat still remains (Steil). In lean horse- 

 flesh Pfliiger found 0-35 per cent, of glycogen, but no sugar. The 

 total nitrogen was 3-21 per cent, of the moist tissue. 



It would be natural to expect that the proteids, which 

 bulk so largely among the solids of the dead muscle, and 

 which are so obviously important in the living muscle, 

 should be affected by contraction. But up to the present 

 time no quantitative difference in the proteids of resting and 

 exhausted muscle has ever been made out. The following 

 chemical changes, however, have been definitely established. 

 In an active muscle 



(a\ More carbon dioxide is produced. 

 () More oxygen is consumed. 



(c) Sarcolactic acid is formed. 



(d) Glycogen is used up. 



(e) The substances soluble in water diminish in amount ; those 



soluble in alcohol increase. 



That the carbon dioxide is not formed by direct oxida- 

 tion, but by the splitting up of a substance or substances 

 with which the oxygen has previously combined, is, as has 

 already been shown (pp. 247, 248), highly probable. For (to 

 recapitulate) (a) no free oxygen exists in muscle. None can 

 be pumped out. (6) A frog's muscle isolated from the body 

 will go on contracting for a long time in an atmosphere 

 devoid of oxygen, e.g., in an atmosphere of hydrogen. 

 (c) When artificial circulation is maintained through isolated 

 muscles, the amount of carbon dioxide produced does not 

 run parallel with the quantity of oxygen consumed. The 



