42 HUMAN PHYSIOLOGY 



nesium, calcium, and iron. But a part of the phosphoric 

 acid is derived from the phosphorus of the nuclei of 

 muscle, and probably from phosphocarnic acid. 



1. Proteids. Of the organic constituents, by far the 

 greater part is made up of Proteids. These may be divided 

 into 



(a) Those soluble in neutral salt solutions. 

 (6) Those insoluble in them. 



(a) The first class of bodies consist entirely of three 

 globulins. Two of these Myosinogen and Paramyosinogen 

 have the peculiar property of clotting under certain condi- 

 tions, of forming what is called Myosin, and this process, 

 which occurs after death, is the cause of death stiffen- 

 ing. The post-mortem change is supposed to be brought 

 about by the development of an enzyme, since a glycerine 

 extract of dried muscle rapidly causes the formation of 

 myosin. The third globulin, Myoglobulin, does not undergo 

 this change. These three proteids are contained in the 

 plasma the juice which can be expressed from muscles kept 

 near the freezing point. If the plasma is warmed it rapidly 

 forms a jelly, clots just as it does post mortem. 



(b) The insoluble proteid of muscle, Myostromin, seems 

 to be in the nature of a nuclein, and probably forms the 

 framework of the fibres. It is always mixed with the 

 collagen of the fibrous tissue of muscle, and it may be 

 separated by dissolving in carbonate of soda solution. (See 

 Chemical Physiology, p. 6.) 



Collagen of the fibrous tissue holding the muscle fibres 

 together is also present, and yields gelatin. 



In addition to the proteids, small quantities of other 

 organic substances are found in muscle. 



2. Carbohydrates. Glucose (C 6 H 12 6 ) is present in muscle, 

 as in all other tissues. 



Glycogen #(C 5 H 10 O 5 ) a substance closely allied to ordi- 

 nary starch, but giving a brown reaction with iodine is 

 always present in muscle at rest. If the muscle has been 

 active, the amount of glycogen diminishes, being probably 

 converted to glucose, and used for the nourishment of the 

 tissue. (For the chemistry of these, see p. 316.) 



