64 CHEMICAL CHANGES. [BOOK i. 



Chemical Changes. 



Before we attack the important problem, What are the chemical 

 changes concerned in a muscular contraction? we must study in 

 some detail the chemical features of muscle at rest. And here we 

 are brought face to face with the chemical differences between 

 living and dead muscles. All muscles, within a certain time after 

 removal from the body, or while still within the body, after 

 'general' death of the body, lose their irritability. The loss of 

 irritability, even when rapid, is gradual, but is succeeded by an 

 "^event which is somewhat more sudden, viz. the entrance into the 

 condition known as rigor mortis, the occurrence of which is marked 

 by the following features. The muscle, previously possessing a 



r certain translucency, becomes much more opaque. Previously very 

 extensible and elastic, it becomes much less extensible and at the 

 same time loses its elasticity; the muscle now requires considerable 

 force to stretch it, and when the force is removed, does not, as 

 before, return to its natural length. To the touch it has lost much 

 of its former softness, and becomes firmer and more resistent. The 

 entrance into rigor mortis is characterised by a shortening or con- 

 traction, which may, under certain circumstances, be considerable. 

 The energy of this contraction is not great, so that when opposed, 

 no actual shortening takes place. When rigor mortis has been fully 

 developed, no muscle-currents whatever are observed. The onset 

 of this rigidity may be considered as the token of the death of the 

 muscle itself. As we shall see, the chemical features of the dead 

 rigid muscle are strikingly different from those of the living 

 muscle. 



If a dead muscle, from which all fat, tendon, fascia, and con- 

 nective tissue have been as much as possible removed, and which 

 has been freed from blood by the injection of saline solution, be 

 minced and repeatedly washed with water, the washings will 

 contain certain forms of albumin and certain extractive bodies, 

 of which we shall speak directly. When the washing has been 

 continued until the wash-water gives no proteid reaction, a large 

 portion of muscle will still remain undissolved. If this be treated 

 with a 10 p. c. solution of a neutral salt, ammonium chloride being 

 the best, a large portion of it will become imperfectly dissolved 

 into a viscid fluid which filters with difficulty. If the viscid 

 filtrate be allowed to fall drop by drop into a large quantity of 

 distilled water, a white flocculent matter will be precipitated. 

 This flocculent precipitate is myosin. It is a proteid, giving the 

 ordinary proteid reactions, and having the same general elementary 

 composition as other proteids. It is soluble in dilute saline solutions, 

 especially those of ammonium chloride, and may be classed in 

 the globulin family, though it is not so soluble as paraglobulin. 

 Dissolved in saline solutions it readily coagulates when heated, i.'e. 



