134 STUDIES IN ADVANCED PHYSIOLOGY. 



This wave of negative variation referred to occurs in liv- 

 ing muscle, and its presence there may be indicated by a 

 sensitive galvanometer. The rate of this wave has been 

 measured, and is in the muscles of mammals about three 

 meters per second. The time required for this wave to 

 traverse the entire muscle is only about one three-hun- 

 dredths of a second. As the latent period is about one one- 

 hundredth of a second, this wave of negative variation is 

 entirely over before the wave of contraction follows. 



This wave then has physiological meaning. The deflec- 

 tion of the magnetic needle connected with the muscle in- 

 dicates that there are going on in this latent period peculiar 

 molecular changes, the nature of which we do not yet at all 

 understand, but which get the muscle ready for the con- 

 traction which follows just an instant later. This wave run- 

 ning along a muscle may be actually used to stimulate the 

 nerve of another muscle. If, for instance, two muscles 

 with their nerves intact be removed from a frog, which 

 muscles we will call here A and B, and the nerve of A be 

 laid on the muscle of B, and then the nerve of B stimulated 

 so that B will contract, it is found that not only does B con- 

 tract, but A contracts also. This is explained in this way: 

 "Every time B is stimulated by its nerve a wave of negative 

 variation runs along it, which wave acts as an electrical 

 stimulus to the nerve of A which rests on it, and so the 

 nerve of A, being stimulated, produces a contraction of the 

 muscle of A. If, then, B is tetanized, a corresponding te- 

 tanus is produced in A, showing that each single impulse 

 has its own wave of negative variation preceding it. 



Rigor Mortis, or Death-Stiffening. 



Soon after death, varying from a few minutes to not 

 more than several hours, the muscles of the body become 

 intensely rigid, preventing the bending at the joints, a con- 

 dition familiar as ' ' death-stiffening, ' ' or rigor mortis. This 

 rigor begins as a rule in the muscles of the lower jaw and 

 neck, then seizes the upper extremities and gradually ex- 



