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greatest difficulty, and it does not, at present, seem to me possible to give any 

 evidence of a more direct nature than that stated above. Nevertheless, the 

 deductions that can be made from the conclusion there reached are so sug- 

 gestive, that they may almost be taken as the strongest evidence in favour of 

 the view that the impulse actually travels down the spiral. 



Before considering these, however, the path of the impulse may be further 

 discussed. If, as seems probable, the impulse travels along the spiral, it becomes 

 possible, to decide on what part of the spiral it travels. It is well known, that 

 if the muscle from an animal be placed for about ten minutes in water, the 

 muscle, while remaining capable of transmitting excitatory impulses, ceases to 

 be able to respond to these by contracting. That part of the spiral which is 

 concerned with contraction has evidently been destroyed ; the conducting portion 

 has remained unaffected. When histological preparations are made of a muscle 

 thus treated, I find that the darkly-staining material has been destroyed ; Krause's 

 membrane remains perfectly intact. From this it would follow that it is the 

 spiral Krause's membrane along which the stimulus travels within the muscle 

 fibre, and that the dark material is concerned solely with contraction. 



There is some other curious evidence in favour of this view. I have pointed 

 out in my previous paper, that the motor end plate nuclei terminate in con- 

 nection with Krause's membrane. In a remarkable paper by J. F. Fulton 

 (1921), further evidence in favour of this view, as pointed out to me by Mr. H. 

 R. Marston, is to be found. Fulton investigates the action of novocaine on the 

 neuromuscular mechanism ; he finds that this drug which acts physiologically, 

 like curare, in paralysing the end plates, accumulates within the end plate 

 nuclei, where its presence can be detected by forming subsequently brown diazo 

 compounds with metaphenylenediamine. Since these nuclei lie in connection 

 with Krause's membrane which, as I have shown above, is the only part of the 

 spiral that remains in "water-logged" muscle ; and since the nerve fibrils actually 

 appear to communicate with these nuclei, and since, finally, novocaine, which 

 paralyses the myoneural junction, acts directly on these nuclei, it would seem 

 that the chain of evidence is fairly complete, which shows that the stimuli, travel- 

 ling down the terminal nerve fibres, pass through the nuclei, and, entering Krause's 

 membrane, travel along this membrane to the ends of the fibre. 



This stimulus can be shown, by observing the contractile wave, to be capable 

 of travelling in both directions within the fibre. 



The velocity of a muscle wave, and therefore of the impulse which causes 

 it, has been shown to be, in the frog, 3 to 4 metres per second (gastrocnemius 

 muscle) ; in the mammalian muscle it travels at about 6 metres per second. It 

 follows, since the fibres run along the longitudinal axis of these muscles, that 

 the velocity of the impulse in a straight line along the fibres will be the same. 

 Actually, however, since the impulse travels along the spiral Krause's membrane, 

 the velocity will be very much larger than this, and the velocity with which it 

 travels along the spiral can be calculated if we know the thickness of the fibre and 

 the distance between the striations. These observations are not easy to make, as 

 dead muscle must be avoided, and in living muscle the inherent elasticity of the 

 fibres tends to cause considerable swelling and shortening of these. When, 

 however, muscle tissue is teased up in Ringer's solution and all those fibres 

 which are subjected to artificial stretching, or which have mechanically shortened, 

 due to their elasticity, are excluded, measurements of the remainder should give 

 the required data with considerable accuracy. I cannot confirm the statement 

 often made that the fibres of a muscle show very great variations in their 

 breadth; it should be remembered that, on account of their properties, muscle 

 fibres are very deceiving in this respect. 



