CHEMICAL CHANGES IN MUSCLE 213 



protein, giving rise to a precipitate in dilute solutions, or forming a jelly-like clot in 

 strong solutions. The properties of these proteins may be summarised as follows : 



(1) Myosin (paramyosinogen of Halliburton). A globulin, coagulating at about 47- 

 50C., precipitated by half saturation with ammonium sulphate or oh dialysis. Trans- 

 formed slowly in solution, rapidly on precipitation, into an insoluble protein, myosin 

 fibrin. 



(2) Myogen (myosinogen of Halliburton). A protein allied to the albumens in 

 that it is not precipitated by dialysis. Coagulates on heating at 55-60C. It changes 

 slowly into an insoluble protein, myogen fibrin, but passes through an intermediate 

 soluble stage called soluble myogen fibrin. This latter body coagulates on heating to 

 40C., being instantly converted at this temperature into insoluble myogen fibrin. 

 It does not seem that any ferment action is associated with these changes, which we 

 may represent by the following schema : 



Muscle-plasma. 



I 



I 



1 myosin or paramyosinogen. i myogen (myosinogen of Halliburton, 



albumate of Kiihne). 



Soluble myogen fibrin. 



I 



Myosin fibrin. Insoluble myogen fibrin. 



Muscle clot. 



Soluble myogen fibrin, which in mammalian muscle-plasma forms only on standing, 

 exists apparently preformed in frog's muscle. Hence the instantaneous clotting of 

 's muscle-plasma on warming to 40C. 



The residue left after the expression of the muscle-plasma consists 

 defly of connective tissue, sarcolemma, and nuclei, and as such contains 

 ilatin (or rather collagen), mucin, nuclein, and adherent traces of the 

 proteins of the muscle-plasma itself. 



The muscle-serum contains the greater part of the soluble constituents 

 of muscle. 



OTHER CONSTITUENTS OF MUSCLE. A number of other sub- 

 stances are found in muscle in small quantities, those which are soluble 

 being contained to a great part in the muscle- serum. It will suffice here 

 to enumerate the chief of these. 



t(a) Colour ing -matter. All red muscles contain a considerable amount of haemo- 

 bin. A special muscle pigment allied to haemoglobin has been described by MacMunn 

 as myohaematin. The only evidence for its existence is spectroscopic. 



(b) Nitrogenous extractives. ' Of these, the most important is creatine (C 4 H 9 N 3 2 ) 

 of which 0*2 to 0*3 per cent, may be found in muscle. Its significance will be the subject 

 of consideration later. Other nitrogenous bodies occurring in smaller quantities are 



>xanthine, xanthine, and traces of urea and amino-acids. 



(c) Non-nitrogenous constituents. 

 Fats, in variable amount. 



Olycogen. This substance is invariably found in healthy muscle. Fresh skeletal 

 le contains about 1 per cent. In the embryo the muscles may contain many 



this quantity of glycogen. 



Glucose is present in fresh muscle in minimal quantities, about -01 per cent. 

 When muscle is allowed to stand, especially in a warm place, the glycogen under- 

 goes partial conversion into glucose, so that the latter increases at the expense of the 



