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to it. When one observes the contraction waves in individual fibres, the former 

 is found to be the case. The same is clearly seen in the beautiful figure of a con- 

 traction wave in Dytisciis muscle given by Schafer. 



If we accept the third of these possibilities, then we are faced with this 

 same difficulty; the contraction wave would be expected to advance at an angle 

 (probably of 45 degrees) with the longitudinal axis. Moreover, if the stimulus, 

 according to this view, can travel across the "striation," then, since the "stria- 

 tions" really form a continuous spiral band, there is nothing to limit this passage 

 of the stimulus, and it must continue to travel along the spiral; i.e., we are 

 driven to accept the first of the three possibilities. 



(2) Since the contractile wave marks the path of the excitatory impulse, 

 observations on fixed contractile waves, especially in the region of the motor 

 end plate, should be of great value. It is seldom that one may have the good 

 fortune to fix a muscle fibre at the moment that the impulse is leaving the end 

 plate. Such a case has, however, been observed by Rollett, and his excellent 

 figure is reproduced here. From it we see that the impulse, as marked out by 



Contractile wave in muscle fibre of 

 Cassida cqiicstris, spreading from 

 region of motor end plate. Note the 

 travelling of the wave across the 

 "striations," i.e., along the spiral. 

 (From Jordan and Ferguson's 

 Histology, after Rollett.) 



the contractile wave, is travelling "across the striation," and although the 

 impulse has afifected a number of fibrils in a direction transverse to the length 

 of the fibre, there is no evidence to show that the stiinulus has advanced along 

 the fibrils. Rollett himself regarded the impulse as travelling across the striation 

 in Krause's membrane. But since he was not aware of the arrangement of these 

 striations in spirals he failed to put the obvious interpretation on his results. 



Nevertheless, his figure shows clearly that the impulse is travelling across 

 the striations, and it would appear that the striations beyond the region of the 

 nerve end plate could not become affected, until the stimulus had travelled right 

 across the fibre to the other side, and then back again along the spiral. 



To demonstrate by direct observation the path of the impulse in such 

 nnnute and rapidly acting tissues as muscle fibres is. of course, a matter of the 



