176 . Prof. A. B. Macallum and Miss M. L. Menten. [July 2.4, 



each in 5-per-cent. solution, dissolves out the deposits, beginning first with 

 the annular ring, and proceeding inwards along the axon. Fig. 2, Plate 2, 

 represents preparations in which the earlier stages in this solution have 

 already taken place, and in consequence the precipitate in the immediate 

 vicinity of the node has been removed by the potassium cyanide solution. 



When the preparation was first of all put into cane sugar solution 

 of 5 - 60 per cent, strength, or into a 1'09-per-cent. solution of potassium 

 nitrate,* the shape and general appearance of the fibres were on the whole 

 maintained, but subsequent treatment with the silver reagent gave no silver 

 reaction at tbe nodes. These solutions dissolve out of the nerve fibres, or at 

 least from the neighbourhood of their nodes, the salts they contain, and the 

 sugar or the nitrate diffuses in, with the result that no precipitate of chloride 

 of silver occurs. Also when the fresh preparations are placed for even a 

 couple of minutes in distilled water, there is a considerable diminution in the 

 amount of the silver precipitate at the nodes, though Frommann's lines may 

 be found for a short distance on each side of any one of them. When their 

 stay in distilled water covers as much as 15 minutes, the silver precipitate 

 does not appear at the nodes or elsewhere. 



One may admit that these solutions dissolve out other constituents in 

 addition to chlorides, and consequently the absence of a silver reaction 

 in such a case does not of itself alone point to the chlorides as the necessary 

 factor in the precipitation, but taken in conjunction with the results of the 

 treatment of the unreduced precipitate with solutions of potassium cyanide, 

 sodium thiosulphate, the chlorides of calcium, magnesium, sodium, and 

 potassium, as well as with dilute ammonia, all of which dissolve more or less 

 readily silver chloride, one can but conclude that the precipitate which forms 

 at the nodes is that of chloride of silver. There is, further, the fact that 

 there are no compounds, either inorganic or organic, except the chlorides and 

 creatin and taurin, in the physiological economy which, in the presence 

 of free nitric acid, give with silver salts precipitates which darken in the 

 sunlight, and it is from data supplied by analyses of nerve tissue impossible 

 to regard the silver precipitate of nerve fibres as in part due to either creatin 

 or taurin, or both. 



This conclusion is further fortified by the results of treatment of nerve 

 fibres with the mercurous nitrate reagent, followed, as described in the 

 section on methods, by the application of ammonium sulphide. The reaction 

 depends on the formation of the highly insoluble mercurous chloride and the 

 demonstration of the presence of this precipitate by its conversion into the 



* These solutions are approximately isotonic with 0'64-per-cent. solution of sodium 

 chloride. 



