188 Prof. A. B. Macallum and Miss M. L. Menten. [July 24, 



V. — General Remarks. 



The observations detailed in the foregoing pages make it possible, at least 

 to a certain extent, to understand nerve conductivity, and perhaps also nerve 

 irritability. 



The occurrence of chlorine in the form of chloride or chlorides in the 

 axon, uniformly distributed throughout its extent, may now be regarded as 

 established. The concentration in the axon also is greater than that in the 

 fluid lymph bathing the fibre, for the silver reaction in the elements 

 external to the fibre does not at all approach in intensity that which may be 

 obtained in the axon. As lymph contains not more than 062 per cent, 

 sodium chloride, the concentration in the axon must considerably exceed that. 



If the chlorine is present as more than one chloride compound, then it 

 must be in combination with sodium, calcium, and magnesium, potassium 

 being excluded.* If only one chloride obtains in the axon, it is inferentially 

 that of sodium. 



The chloride or chlorides are, in part at least, in solution in the material 

 constituting the axon, and thus obtains the electrolytic condition which 

 would explain the conductivity of the axon, the propagation of the nerve 

 impulse itself, and apparently also the excitable efficiency of the nerve fibre. 



That all of the chloride or chlorides cannot be in the ordinary state of 

 solution would seem to follow from the facts regarding the velocity of the 

 nerve impulse. If the latter is, fundamentally, an electrical change in 

 the process of being propagated along the axon, it should, provided the 

 chloride or chlorides are in a simple state of solution, have a velocity 

 enormously greater than its maximum has been ascertained to be, that is, 

 64 metres per second. 



On the assumption that the nerve impulse is, fundamentally, electrical, such 

 a diminution in the velocity postulates a disposition of the chloride or 

 chlorides in the axon very different from that in a simple aqueous solution of 

 them. This difference may be attributed to the condition of the colloid 

 material in the axon. 



A " solution " of colloid matter, at least of the organic sort, has, as is well 

 known, properties very unlike those of a solution of a simple inorganic 

 compound, sodium chloride or potassium sulphate, for example, properties 



* Macallum, ' Journ. of Physiol.,' vol. 32, p. 1, 1905. Note. — Macdonald, in a recent 

 contribution (" The Structure and Function of Nerve Fibres,"' Roy. Soc. Proc.,' B, voL 76, 

 p. 322, 1905), holds that potassium is present in a concealed, or " masked," condition in 

 the substance of the axon of the normal fibre, and therefore not demonstrable ordinarily 

 with the heaxanitrite of cobalt and sodium, but that it is set free from the masked 

 condition when the axon is injured. 



