84 THE CONTRACTILE TISSUES. 



shall see, however, the rapidity and completeness of the return depends on 

 the condition of the muscle, a well-nourished active muscle regaining its 

 normal length much more rapidly and completely than a tired and exhausted 

 muscle. A dead rigid muscle is much less extensible, and at the same time 

 much less elastic ; the muscle now requires considerable force to stretch it, 

 and when the force is removed, does riot, as before, return to its former 

 length. To the touch the rigid muscle has lost much of its former softness, 

 and has become firmer and more resistant. The entrance into rigor mortis 

 is, moreover, accompanied by a shortening or contraction, which may, under 

 certain circumstances, be considerable. The energy of this contraction is 

 not great, so that any actual shortening is easily prevented by the presence 

 of even a slight opposing force. 



Now the chemical features of the dead rigid muscle are also strikingly 

 different from those of the living muscle. 



59. If a dead muscle, from which all fat, tendon, fascia, and connec- 

 tive tissue have been as much as possible removed, and which has been 

 freed from blood by the injection of "normal " 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 per cent, solution of a neutral salt, ammonium 

 chloride being the best, a large portion of it will become dissolved ; the 

 solution, however, is more or less imperfect and filters with difficulty. If 

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

 tilled water, a white flocculent matter will be precipitated. This flocculent 

 precipitate is myosin. Myosin 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 ammo- 

 nium chloride, and may be classed in the globulin family, though it is 

 not so soluble as paraglobulin, requiring a stronger solutio"n of a neutral 

 salt to dissolve it ; thus, while soluble in a 5 or 10 per cent, solution of such 

 a salt, it is far less soluble in a 1 per cent, solution, which, as we have seen, 

 readily dissolves paraglobulin. From its solutions in neutral saline solu- 

 tion it is precipitated by saturation with a neutral salt, preferably 

 sodium chloride, and may be purified by being washed with a saturated 

 solution, dissolved again in a weaker solution, and reprecipitated by satu- 

 ration. Dissolved in saline solutions it readily coagulates when heated i. e. y 

 is converted into coagulated proteid and it is worthy of notice that it 

 coagulates at a comparatively low temperature, viz., about 56 C. ; this, 

 it will be remembered, is the temperature at which fibrinogen is coagulated, 

 whereas paraglobulin, serum-albumin, and many other proteids, do not 

 coagulate until a higher temperature (75 C.) is reached. Solutions of 

 myosin are precipitated by alcohol, and the precipitate, as in the case of 

 other proteids, becomes, by continued action of the alcohol, altered into 

 coagulated insoluble proteid. 



We have seen that paraglobulin, and, indeed, any member of the 

 globulin group, is very readily changed by the action of dilute acids into a 

 body called acid-albumin, characterized by not being soluble either in water 

 or in dilute saline solutions, but readily soluble in dilute acids and alkalies, 

 from its solutions in either of which it is precipitated by neutralization, 

 and by the fact that the solutions in dilute acids and alkalies are not coagu- 

 lated by heat. When, therefore, a globulin is dissolved in dilute acid, 

 what takes place is not a mere solution, but a chemical change ; the globulin 

 cannot be got back from the solution, it has been changed into acid-albu- 



