472 MOVEMENTS. 



lar action, presents certain interesting peculiarities. "We 

 will give, however, only the general characters of this ac- 

 tion, without discussing in detail the complicated apparatus 

 employed. 1 



According to Helmholtz, the whole period of a single 

 contraction and relaxation of the gastrocnemius muscle of a 

 frog is a little less than one-third of a second. The muscles 

 of mammals and birds contract more rapidly, but with this 

 exception, the essential characters of the contraction are the 

 same. The following are the periods occupied by these dif- 

 ferent phenomena: 2 



Interval between stimulation and contraction 0"'020 



Contraction 0"'180 



Kelaxation 0"'105 



0"-305 



The duration of the electric current applied to the nerve 

 is only 0"*0008. Contraction, however, does not follow im- 

 mediately, there being an interval, called pose, of about one 

 fiftieth of a second. The contraction then follows, suc- 

 ceeded by gradual relaxation, the former being a little 

 longer than the latter. 



This description represents the contraction of an entire 

 muscle, but does not indicate the changes in form of the in- 

 dividual fibres, a point much more difficult to determine 

 satisfactorily. It is pretty well established, however, that a 

 single fibre, with its irritability unimpaired, becomes con- 

 tracted and swollen at the point where the stimulation is 

 applied. Now, the question is whether, in normal contrac- 

 tion of the fibres in obedience to the natural nervous 

 stimulus, there be a uniform shortening of the whole fibre, 

 a shortening of those portions only that are the seat of the 



1 A very good resume of the general characters of a single muscular con- 

 traction (secousse musculaire) is given by Bernard, in his recent work on the 

 properties of living tissues. (Le$om sur les proprietes des tissus vivants, Paris, 

 1866, p. 193, et seq.) 



2 BERNARD, op. cit., p. 196. 



