390 THE PROPERTIES OF STRIPED MUSCLE. 



of the paralysed limb, into tetanus by faradising the spinal cord, the 

 circulation remaining intact. In this way the paralysed muscles, 

 although inactive, become fatigued. The process of fatigue is tested at 

 regular intervals by direct and indirect stimulation, and it is found 

 that the indirect excitability disappears first. Abelous therefore con- 

 cludes that, as nerve is inexhaustible, the end-organs are more directly 

 affected by the " fatigue substance " than the muscular fibres themselves. 



Death of muscle. When muscle is immersed in boiling water it at 

 once shortens and thickens, losing its elasticity and becoming opaque. 

 In muscle so treated the proteids coagulate, and all functional chemical 

 changes are brought suddenly to an end. This method is therefore fre- 

 quently used for the purpose of ascertaining the chemical condition of a 

 muscle at any desired moment, so far as relates to those constituents 

 which are known not to be affected by boiling temperature. If the 

 temperature of a muscle is raised gradually, the change of form occurs in 

 stages. According to the recent observations of Brodie, a first shorten- 

 ing occurs at 32 C., ceasing at about 40 C.; a second begins at 46 C. 

 and ceases at 50 C.; a third at 56 C., ending at 60 C.; and at 63 C. 

 there is a final shrinking which ceases at 75 C. As these temperatures 

 closely correspond with the temperatures of coagulation of the several 

 proteid bodies contained in muscle, 1 the observations afford better evi- 

 dence than had before been given of the connection of coagulation with 

 the changes produced in a muscle by warming it. But although 

 coagulation may serve to account both for the loss of elasticity and the 

 opacity produced by heat, it does not sufficiently explain its shortening ; 

 nor does there seem to be any reason why, even when the process is very 

 gradual, the successive diminutions of length should not be in part 

 attributed to contractility. The shortening may be a response to the 

 stimulating action of the temperature, and the opacity may be due to 

 coagulation. 



The production of heat rigor is a more simple process than the 

 similar change which occurs spontaneously at a certain time after death 

 true rigor mortis, or, as it is called by German writers, Zeitstarre. 

 The same question, however, presents itself as regards the immediate 

 cause in the two cases, for in rigor mortis we have, on the one hand, 

 shortening which may be compared to the effect of excitation ; on the 

 other, opacity and loss of elasticity, which may be attributed to solidifi- 

 cation of previously fluid constituents of the muscular substance. We 

 will first inquire what grounds there are for supposing that muscle in 

 the process of dying, passes into a state analogous to that produced by 

 excitation. 



The notion that it does so is an old one. Nysten (1811) compared rigor 

 with vital contraction, and spoke of it as the last effort of dying muscle. This 

 vitalistic idea, after holding its ground for more than a generation, was dis- 

 placed by the theory usually attributed to Briicke, that the process is solely 

 one of coagulation. It may be questioned whether Briicke took so exclusive 

 a view as these words imply; but, in any case, the physiologists of thirty 

 years ago were justified by experimental results, in regarding the solidification 

 of myosin as the most important consequence of the cessation of vital activity. 

 Kiihne had shown 2 that a muscle can be kept in a living state, i.e. prevented 



1 See Halliburton's article in vol. i. of the present book, and Yernon's paper in the 

 Journal of Physiology, 1899. 



2 "Lehrbuch der physiologischen Chemie," 1866, S. 274, 285. 



