1905.] Distribution of Chlorides in Nerve Cells and Fibres. 175 



cipitated is demonstrated by only one-twelfth of its quantity developed as 

 subchloride. 



The preparation of the reagent is that described by Fresenius :* one part of 

 pure nitric acid of 1'2 specific gravity is poured on one part of pure mercury, 

 and the containing vessel is allowed to stand 24 hours in a cool place. The 

 crystals formed are separated from the undissolved mercury and the mother 

 liquor, and, after trituration in a mortar, dissolved in water mixed with one- 

 sixteenth part of nitric acid. The solution, which must be saturated, is 

 filtered, and the filtrate is kept in contact with metallic mercury. When 

 the reagent is to be used, one part of the solution is diluted with three parts 

 of water. 



The reagent is applied to the teased-out nerve fibres, and left in contact 

 with them for half an hour, after which they are washed in distilled 

 water, frequently changed for about two to three hours, and finally mounted 

 in a mixture of 50 per cent, glycerine and ammonium sulphide, which latter 

 converts the white mercurous chloride precipitate into black mercuric 

 sulphide. If it is properly washed with water to remove the precipitant, 

 the final reaction should indicate the distribution of the chlorides. 



The results obtained by the use of this reagent corroborated the con- 

 clusions drawn from the results of the use of the nitrate of silv.v. As 

 a reagent for the detection of chlorides it is not a ready penetrant of 

 tissues, and this cannot be overcome by the addition of an acid, as the 

 latter is apt to convert it into the mercuric salt, which is not a precipitant 

 for chlorides. 



lY.— The Results. 



A. In Nerve Fibre. — If one places a teased-out portion of the sciatic 

 nerve of a frog, guinea-pig, or rat in the silver reagent for about half an 

 hour, and then, without further treatment, in the sunlight, inspection under 

 the microscope reveals the occurrence in the fibres of the appearances known 

 as the crosses of Eanvier, structures which are due to a deposit of silver 

 chloride in the annular ring of the node and in the axon in the immediate 

 vicinity of the ring, the silver chloride on reduction having a dark brown, or 

 sepia, or even black colour. There is no evidence in such preparations of 

 chlorides in other parts of the axons. That the crosses are due to the 

 precipitation at those points of chlorides is shown by the fact that the 

 reagents which dissolve silver chloride also dissolve this deposit before it is 

 reduced by light. For example, calcium chloride, magnesium chloride, 

 sodium thiosulphate, potassium cyanide and potassium and sodium chlorides, 



* 'Manual of Qualitative Chemical Analysis,' American Edition, 1898, p. 111. 



