CHEMICAL PHENOMENA OF MUSCULAR CONTRACTION 753 



limbs in rigor is the same as at death; the muscles stiffen without 

 any marked contraction. This can be strikingly shown on a newly- 

 killed animal by cutting the tendons of the extensors of one foot 

 and the flexors of the other ; when natural rigor comes on, the feet 

 remain just as they were. If heat rigor, however, is caused, the 

 one foot becomes rigid in flexion and the other in extension; and 

 the contraction-force is considerable, although not so great as that 

 of an electrical tetanus in a living muscle. 



The Possibility of Recovery of Muscles after Rigor. When the circu- 

 lation in the hind legs of rabbits is interrupted by compression or 

 ligation of the abdominal aorta (Stenson's experiment), the muscles lose 

 their excitability, but speedily recover, if they have not been deprived 

 of arterial blood for too long a time, when the blood is again allowed to 

 reach them. A longer interruption of the circulation leads not only 

 to total inability to respond to stimulation, but also to rigor, and most 

 observers are agreed that, as regards the skeletal muscles at least, this 

 is the irrevocable end of excitability. Brown-Sequard, indeed, stated 

 that after the full development of rigor in the rabbit's muscles (Stenson's 

 experiment), and also in the hand of an executed criminal through 

 which an artificial circulation was established, recovery ensued. But 

 probably the rigor was incomplete or did not involve all the fibres. In 

 heart muscle the conditions appear to be somewhat different, and Heubel 

 has alleged that rhythmical contractions of the frog's heart can be 

 restored by filling its cavity with blood, after rigor has been caused by 

 heat and in other ways, and we have already seen that the same is true 

 of the mammalian heart alter the onset of rigor. Excised frog's 

 muscles which have undergone rigor mortis become less stiff when 

 exposed to an atmosphere of oxygen. 



