CHEMISTRY OF MUSCLE. 125 



nitrogenous crystalline compounds, especially kreatin I 

 (C4H9N302). As in the case of all other physiologically ac- ' 

 tive tissues, however, the main post mortem constituents of 

 the muscular fibres are proteid substances, and it is proba- 

 ble that like protoplasm itself (p. 24) the essential con- 

 tractile part of the tissue consists of a complex body con- 

 taining proteid, carbohydrate and fatty residues; and that 

 during muscular worktKTsls broken up, yielding proteins , / 



\ -carbonjik^lde, sarcolactic acid, and probably other 

 things; for this hypothetical substance, which has never 

 yet been isolated, the name inonen^ has been proposed. 

 The main proteid substance obtained from muscles is that 

 known as myosin, which is prepared as follows. Perfectly 

 fresh and still living muscles are cut oat from a frog which 

 has just been killed by destruction of its brain and spinal 

 cord, a proceeding which entirely deprives the animal of 

 consciousness and the power of using its muscles, but 

 leaves these latter unaltered and alive for some time. The 

 excised muscles are thrown into a vessel cooled below C. 

 by a freezing mixture and so are frozen hard before any 

 great chemical change has had time to occur in them. The 

 solidified muscles are then cut up into thin slices, the bits 

 thrown on a cooled filter and let gradually warm up to the 

 "freezing point of water, with the addition of some ice-cold 

 0.5 per cent solution of common salt. Gradually a small 

 quantity of a tenacious liquid filters through, which is at 

 first alkaline to test-paper but soon sets into a jelly and 

 becomes acid. The coagulation and the acidity are due to I 

 the breaking up of the muscle substance into the myosin ( 

 and other bodies referred to above. At first the jelly is 

 transparent, but soon the myosin becomes opaque and 

 \ shrinks just like blood fibrin, squeezing out a quantity of 



I muscle serum, and remaining itself as the muscle clot. 

 Myosin thus prepared is insoluble in water and in saturated 

 solution of common salt, but soluble in five or ten per cent 

 watery solutions of the latter substance. When boiled it 

 is turned into coagulated proteid (p. 11) and becomes in- 

 soluble in dilute acids, though myosin itself dissolves 

 in them easily, being at the same time converted into 



