1906.] The Structure of Nerve-fibres. 15 



the basic dye is itself added in increased quantity, then toluidine blue may 

 be made to reveal the complete set of appearances. In these solutions the 

 invasion of the homogeneous region may be watched in a nerve-fibre in which 

 the sudden appearance of granule formation in more distal regions and the 

 intensely stained coagulum is also marked. If, on the contrary, Einger's 

 solution is substituted for " normal saline " in the case of neutral red, 

 nothing whatever, or at the most only faint traces of granule formation are 

 obtained even in the region near to the cut end. The neutral red stain 

 is enabled to penetrate the whole nerve-fibre best when present in small 

 quantity, 0*01 per cent., and when presented in unboiled "normal saline" 

 rendered faintly acid by the presence of carbonic acid. Toluidine blue 

 solution must be rendered faintly alkaline, or, at least, the calcic phosphate 

 of the Einger's solution must be present to prevent a development of acidity. 

 Neutral red is, on the other hand, ineffectual in the presence of a reagent, 

 preventing the development of acidity, and can be made to stain the distal 

 coagulated stretch of the fibre only when presented in association with a 

 slight trace of acid. There is an obvious conclusion to be drawn from this 

 series of facts. 



There is one region of the nerve which neutral red stains when unaided by 

 any addition of acid. This is the point of actual injury, and a limited region 

 in its neighbourhood which gradually extends with lapse of time. The 

 inference is clear, that this is a tract of the nerve in which a certain amount 

 of acidity develops, or, at least, that it is the least alkaline portion of the 

 nerve. The behaviour of toluidine blue in the same region is also seen to 

 support this inference. Here it refuses to stain until alkalinity is obtained. 

 This might lead to the additional inference, that the region of coagulation 

 which toluidine blue stains unaided is itself more alkaline than any other 

 tract of the fibre. 



It would seem therefore that at present we had done no more than map 

 out the teased nerve-fibre into regions of homogeneity and of coagulation, into 

 regions of less and greater alkalinity, and also that we have associated these 

 two separate attributes. There is a homogeneous region close to each injured 

 point which is gradually invaded and rendered granular by an acid tide 

 sweeping in from the point of injury. There is a more alkaline region, in 

 which different grades of coagulation occur. 



The Distribution of Potassium Salts in Teased Nerve-fibres. 



I have already pointed out that Macallum's reagent may be used to prove 

 the existence of potassium in every portion of the length of a nerve-fibre 



