1905.] Distribution of Chlorides in Nerve Cells and Fibres. 177 



black mercuric sulphide. When care is taken in using this method, the 

 results, which will be more fully described below, are curiously like those which 

 the silver reagent furnishes (figs. 10 and 11, Plate 3). 



That the darkened silver precipitate is not metallic silver is shown by the 

 fact that it is soluble in solutions of potassium cyanide, but insoluble in dilute 

 nitric acid, which latter reagent readily dissolves metallic silver. These 

 results indicate that the reduced silver compound in the nerve fibre reacts in 

 the same manner as does the subchloride of silver when similarly treated in 

 the test tube. 



When nerve fibres are left for a longer time than half an hour, for example, 

 24 hours, in the silver reagent, the reaction is found to cover a greater extent 

 of the fibre, and it may occasionally happen that it extends over nearly all an 

 internodal segment, leaving only a slight extent of the axon, midway between 

 two nodes, unaffected. Here one may see the lines of Frommann very 

 distinct, and one finds invariably also that each of the dark strire increases in 

 superficial area with the distance from the node, but at the same time they 

 diminish in the intensity of their tint, and are separated from each other by 

 wider interstriate zones. This result would appear to be due to two causes, 

 one of which is that, remote from the nodes of Ranvier, the axon swells 

 to several times the diameter of the axon at the node, and the other that 

 the reagent, which mainly attacks the axon through the node, becomes more 

 dilute as it penetrates. This dilution of the reagent, which affects only the 

 silver salt, not the acid, robs it of its fixing power, and thus promotes its 

 distending effect on the axons. Sometimes there is found the further result, 

 represented in fig. 1, a, where the chlorides are diffused from the swollen axon 

 into the immediately adjacent medulla, and consequently Frommann's lines 

 fail to appear there. This result may be, and often is, much more pronounced 

 in preparations treated with a decinormal solution of silver nitrate containing 

 from 5 to 10 per cent, of free nitric acid. An example of this is represented 

 in fig. 8, where the medulla of the parts remote from the nodes is shown 

 impregnated throughout with chlorides diffused from the axon. 



It is, therefore, at the nodes and in their immediate vicinity that one obtains 

 always, or nearly always, the best silver chloride reaction, regard being had 

 to the character and disposition of the precipitate, and to the proper fixation 

 of the axon, and it is also in the neighbourhood of the nodes that one finds, 

 after treatment of nerve fibre with the silver reagent, the most typical 

 examples of Frommann's lines. 



To get the reaction extend as far as possible along the axon, one must 

 treat the nerve fibres with a decinormal solution of silver nitrate in which 

 the strength of the acid has been increased to 10 per cent. Acted on for four 



