472 MANUAL OF PHYSIOLOGY. 



postpones the appearance of the changes in the muscles upon which 

 rigor depends. (4.) Stretching, or any mechanical excitation 

 which tends to injure or hasten the death of the tissue, causes it 

 to pass more rapidly into rigor. (5.) The application of water 

 and of a number of chemical substances causes muscles quickly to 

 pass into a state of rigor similar in all essential respects to that 

 which ordinarily follows the death of the tissue. (6.) Any stop- 

 page in the blood-current normally flowing through a muscle, 

 after some little time makes it pass into a state of rigidity like 

 rigor mortis, but this may be removed by allowing the blood to 

 flow freely again through the muscle. 



It is generally admitted that muscle rigor depends on the coag. 

 ulation of the muscle plasma, giving rise to myosin and muscle 

 serum. This is in most respects comparable with the coagulation 

 of the blood, and also seems to be produced by the action of some 

 ferment, of which several have been made out in dead muscle tis- 

 sue (compare the par. on chemistry, p. 442). 



Most of the phenomena of the process of muscle rigor remind 

 us of the changes which were noted as occurring in muscle when 

 it passes from the passive to the active state. Thus the shortening 

 of the fibres, the evolution of heat, and the chemical changes may 

 be said to be identical in contraction and rigor mortis. The elec- 

 trical changes are, however, very transitory, and are followed by 

 complete loss of elasticity and irritability. Opacity of the tissue 

 accompanies its later stages. 



Thus, while dying, the muscle tissue may be said to go through 

 a series of events analogous to those which would occur in a pro- 

 longed contraction without any period of recuperation. The idea 

 naturally has suggested itself to the minds of physiologists that 

 the active state of muscle depends upon chemical changes which 

 are the initial steps in the coagulation of the contractile substance, 

 when the muscle is dying. The muscle tissue is supposed to con- 

 tain a special proteid of extremely intricate and unstable chemical 

 constitution, which, like all plasmata, is constantly undergoing 

 slow molecular change, and which if not reintegrated by constant 

 assimilation would pass into coagulation. Under the influence of 

 stimuli a comparatively sudden and intense molecular disturbance 



