208 VETERINARY PHYSIOLOGY 



the proteins, and which coagulates at between o5° and 

 65° C. 



(h) Paramyosinogen, which constitutes about 13 per cent., 

 and coagulates at 46° to 51° C. 



Both of these, after the death of the muscle, change into 

 an insoluble form, Myosin. In the case of myosinogen this 

 takes place in two stages — first, the formation of a soluble 

 myosin, coagulating at a very low temperature — 35° to 40° C. ; 

 and second, the insoluble m3^osin. The soluble myosin exists 

 preformed in the muscles of cold-blooded animals. 



(c) Myoglobulin, another globulin which does not clot, is 

 present in the muscles of fish and amphibia. 



Whether such separate proteins actually exist in living 

 muscle, or whether they are the result of some change in 

 the colloidal complex at death, it is impossible to say, but 

 the fact that the living muscle when gradually heated 

 undergoes a sharp shortening at the temperatures at which 

 these proteins coagulate favours the view that they do 

 exist. 



(2) The insoluble protein of muscle, Myostromin, seems 

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

 framework of the fibrils. 



(3) In the residue after extraction of the globulins, it is 

 always mixed with the Collagen of the fibrous tissue of 

 muscle, from which it may be separated by dissolving it in- 

 carbonate of soda solution, and reprecipitating by weak acetic 

 acid (Chemical Physiology). 



2. In addition to the proteins, small quantities of other 

 organic substances are found in muscle — 



(1) Carbohydrates. — Glucose (CgH^^Oe) is present in muscle, 

 as in all other tissues. 



Glycogen ^(CelljoOg) — a substance closely allied to 

 ordinary starch, but giving a brown reaction with iodine — is 

 always present in muscle at rest. The amount is variable 

 from 0'3 to 1"0 per cent., but the mass of muscle is so 

 great that about one-half of all the glycogen of the body is 

 in the muscles, the rest being chiefly in the liver. If the 

 muscle has been active, the glycogen diminishes, being 

 probably converted to glucose, and used for the nourishment 



