SECONDARY PULSATION AND TETANUS. 209 



in uninjured animals, lent force to this explanation. 

 Yet no sufficiently strong proof of this view has been 

 brouofht forward to cause us to doubt the existence of 

 electric action in uninjured and living muscles. 



The question does not, however, essentially affect 

 the physiological conception of the relation of this ac- 

 tivity to the other vital qualities. It is unimportant 

 w^hether the separate portions of the outer surface of 

 a muscle are similar or dissimilar in the matter of ten- 

 sion. The only essential point is, as to whether electro- 

 motive forces are present within the muscle, and whether 

 these are in any way related to the physiological work 

 of the muscle. Negative variation has a deeply impor- 

 tant bearing on this question, so that we will, after this 

 digression, return to a more detailed study of this 

 phenomenon. 



4. It is unnecessary to tetanise the muscle in order 

 to exhibit negative variation. If a sufficiently sensitive 

 multiplier is used, a single pulsation suffices. Even 

 without a multiplier, negative variation may be very 

 well shown in the following way. 



On a gastrocnemius prepared with its nerve (fig. 57), 

 or on an entire thigh (5, fig. 58), the nerve of a second 

 gastrocnemius, or thigh. A, is placed in such a way 

 that one part of the nerve touches the tendon, another 

 part touches the surface of the muscle-fibres. The nerve 

 then represents a sort of applied arch, uniting the nega- 

 tive cross- section and the positive longitudinal section, 

 and a current, corresponding with the difference of ten- 

 sion at these points of contact, passes through the nerve.* 



' This current may at the moment of i'.s generation, i.e. on Vne 

 sudden appli< nation of the nerve, exercise an irritating effect on 

 the nerve and may elicit a pulsation of the muscle. This is tV.e 



