MUSCLE 585 



given amount of muscular work requires the expenditure 

 of approximately the same quantity of chemical energy, 

 whether it comes almost entirely from proteid, or chiefly 

 from carbohydrates, or chiefly from fat. Some observers have 

 stated that the taking of even a comparatively small quantity 

 of sugar vastly increases the capacity for muscular work as 

 measured by the ergograph (p. 621). But although it is not 

 to be doubted that sugar is under normal circumstances one 

 of the most important substances used up in muscular con- 

 traction, the claim that sugar is, par excellence, the food for 

 muscular exertion has not yet been made out. 



Eigor Mortis. When a muscle is dying its excitability, 

 after perhaps a temporary rise at the beginning, diminishes 

 more and more until it ultimately responds to no stimulus, 

 however strong. The loss of excitability is not in itself a 

 sure mark of death, for, as we have seen, an inexcitable 

 muscle may be partially or completely restored ; but it is 

 followed, or, where the death of the muscle takes place 

 very rapidly, perhaps accompanied, by a more decisive 

 event, the appearance of rigor. The muscle, which was 

 before soft and at the same time elastic to the touch, 

 becomes firm ; but its elasticity is gone. The fibres are no 

 longer translucent, but opaque and turbid. If shortening 

 of the muscle has not been opposed, it may be somewhat 

 contracted, although the absolute force of this contraction 

 is small compared with that of a living muscle, and a slight 

 resistance is enough to prevent it. The reaction is now 

 distinctly acid to litmus. This is rigor mortis, the death- 

 stiffening of muscle. 



An insight into the real meaning of this singular and 

 sometimes sudden change was first given by the experiments 

 of Kiihne. He took living frog's muscle, freed from blood, 

 froze it, and minced it in the frozen state. The pieces were 

 then rubbed up in a mortar with snow containing i per cent, 

 of common salt, and a thick neutral or alkaline liquid, the 

 muscle-plasma, was obtained by filtration. This clotted 

 into a jelly when the temperature was allowed to rise, but 

 at o C. remained fluid. The clotting was accompanied by 

 a change of reaction, the liquid becoming acid. An equally 



