THERMAL AND CHEMICAL CHANGES IN MUSCLE 555 



muscular contraction has afforded valuable information. The pheno- 

 menon of contraction has also been studied from the point of view of 

 the osmotic properties of the muscle. 



It has been suggested, after due consideration of the time relations 

 of the contraction and the distance in the fibril through which osmotic 

 force has to act, that muscular contraction may be brought about 

 by this force. Provisionally, we may suppose that lactic acid is set 

 free, and that combines with protein to form a salt, with a conse- 

 quent rise of osmotic pressure in the dim bands of the muscle fibrils, 

 which therefore swell at the expense of the water in the light bands. 

 Granting that this may be so, we do not know how the osmotic equi- 

 librium is upset by the stimulus or restored during relaxation. 



The Changes in the Chemistry of Muscle 1. The Chemical Con- 

 stitution of Muscle. If muscle be taken from an animal and minced, 

 and then squeezed, a plasma can be expressed from it. This, like 

 blood, possesses the property of coagulating at body temperature 

 under suitable conditions. 



Upon analysis, it contains from 75 to 78 per cent', of water, 20 to 

 24 per cent, of organic and about 1 to 2 per cent, of inorganic bodies. 

 The chief organic bodies are the proteins, of which there are from 

 18 to 20 per cent. Various classifications and names have been given 

 to these proteins, which apparently vary in their properties according 

 to their method of preparation, the species of animal used (mammals, 

 birds, reptilia, etc.), the condition of the muscle at the time of death, 

 and the degree of post-mortem changes. To illustrate the chaos 

 which pervades the nomenclature of these proteins, it may be men- 

 tioned that the name " myosin " has been given by different in- 

 vestigators to at least three different bodies. 



The most generally accepted classification of theie proteins is 

 into (1) Myosin, or paramyosinogen, which forms about one-fifth; 

 and (2) myogen, or myosinogen, which forms the other four-fifths 

 Traces of albumin and globulin are also present, but these probably 

 come from the blood and lymph, and not from the muscle proper. 



In the plasma of " red " muscles the colouring matter is also present. 

 'This consists of haemoglobin or a closely allied compound protein 

 myohsematin. 



Myosin, or paramyosinogen, is a globulin soluble in dilute salt 

 solutions which coagulates on heating at about 45 to 50 C. It is 

 .precipitated by weak acids, dialysis, half-saturation with ammonium 

 sulphate, etc., and gives the other reactions characteristic of globulins 

 .(see p. 51). It is characterized by its power of passing at body tempera- 

 ture probably under the influence of an enzyme derived from the 

 muscle directly into an insoluble modification known as myosin fibrin. 



MYOSIX 

 (by enzymic action) 



MYOSIN FIBRIN. 



