i GENERAL PHYSIOLOGY OF MUSCLE 41 



tissue. It seems to us not improbable that the development of 

 fatty acids contributes to the acidification of muscle during its 

 death. 



The inorganic compounds of muscle are water and the salts 

 contained in the ash. 



The amount of water in human muscle is not less than 70 per 

 cent and may rise to 72-74 per cent. It varies to some extent 

 in different classes of muscle. Generally speaking, embryonic 

 muscles and those of young persons are richer in water than 

 those of adults and old people. During starvation the water 

 diminishes considerably ; it is increased, on the contrary, by work, 

 which suggests that during the discharge of the energy accumu- 

 lated in the muscle water is one of the end-products of the carbo- 

 hydrate metabolism. 



Of the mineral salts contained in the ash of muscle the pre- 

 dominance of potash over soda among the bases, and of phosphoric 

 acid among the acids, is remarkable. According to Bunge the 

 ash of 100 parts of muscle contains on an average : 



KjO . . . 4-407 Fe 2 3 . . . O057 



Na 2 . . . 0-790 P 9 3 . . . 4'612 



C.,0 . . . 0-079 01 ... 0-682 



MgO . . . 0-396 S0 3 . . . 0-100 



It is certain that in living muscle these mineral compounds are 

 not all present in the form of simple solutions, but are in organic 

 combination. The sulphuric acid is formed from the sulphur of 

 the proteins during combustion. The phosphoric acid is only pre- 

 existent to a very small extent in living muscle, the greater part 

 arises from the combustion of the lecithin and the nucleins. 

 The ferric oxide results from the disintegration of the muscular 

 haemoglobin. 



The gases of muscle consist in a considerable amount of carbon 

 dioxide and traces of nitrogen. The mercury pump has failed 

 to separate any trace of oxygen from muscles when carefully 

 washed free of blood, obviously because the oxygen combined with 

 the haemoglobin is dissociated and carried away in the washing. 

 According to Hermann (1867), 2 pl 74-' per cent free, and 1*95 

 per cent combined C0 2 can be extracted from muscle which is 

 bled, minced up, and triturated previous to the onset of rigor. 

 Stintzing found that on prolonged boiling of muscle another 

 substance decomposes, which gives rise to a free development of 

 C0 2 . It is probable that the carbonic acid developed in tetanus 

 and during rigor is derived from the same substance as is decom- 

 posed by boiling. 



We have already reviewed the principal facts of muscular 

 respiration (Vol. I. p. 393). The important fact is that the gas 

 exchanges of muscle are exaggerated during activity, i.e. both 



