S56 BIOLOGY. [BOOK v. 



which gives to the muscular juice its alkaline reaction. In pro- 

 portion as a muscle is fatigued its reaction becomes less and less 

 alkaline, and finally passes into acidity. At the same time the 

 muscle furnishes a quantity greater and greater of soluble sub- 

 stances. According to Helmholtz, there is in a fatigued muscle 

 0'73 per cent, of parts soluble in water: there is only 0'65 per 

 cent, in a muscle which has rested. 



Some hours after death the muscle becomes rigid. It is then 

 spoken of as in a state of cadaveric tenseness, which seems due to 

 the spontaneous coagulation of the contractile or syntonine sub- 

 stance ; for we can provoke the rigid state by plunging a muscle 

 into a liquid at 45 degrees. 1 



At the outset we can also make the rigidity disappear by 

 letting a sanguineous current pass into the vessels. 



As the muscle in cadaveric rigidity generally offers an acid 

 reaction due to the lactic acid, it has been believed that the 

 coagulation of the syntonine was due to the presence of the 

 acid ; but Cl. Bernard saw in crabs the muscles of the tail in a 

 state of cadaveric rigidity, though they still presented an alka- 

 line reaction. Finally, he observed that the acid reaction is 

 often lacking in the bodies of animals that have died after a 

 long abstinence. 



We have already remarked that muscular irritability is a 

 property inherent in the muscular element, wholly distinct from 

 the excitant which brings it into play, without excepting the 

 most important of those excitants, the nervous system. The 

 fact is demonstrated either by killing the excito-motory nervous 

 fibres, as we do, for instance, by means of the curare* poison, or 

 inversely by abolishing the contractility of the fibre, with the 

 help of certain substances which do not act on the nerves. The 

 muscular poisons the most in use are the sulpho-cyanuret of 

 potassium, the sulphate of copper, tne sulphate of mercury, and 

 also certain organic poisons which act first of all on the 



1 Cl. Bernard, loc. tit., p. 230. 



