1905.] Distribution of Chlorides in Nerve Cells and Fibres. 179 



feature is the penetration, by even the weaker reagent, of long sections of 

 such fibres in as short a period as an hour, an interval of action on nerve 

 fibre with neurilemmal sheaths which would allow only of the demonstration 

 of little more than sufficient to bring out the crosses of Eanvier. 



In support of the view that the neurilemma acts as a very considerable 

 barrier to the penetration of nitrate of silver, the results of observations on 

 nerve fibres of invertebrates may be detailed. In the decapod Crustacea 

 (lobster and crayfish) the nerve fibres of the ganglionic cord are ensheathed 

 each in membranes which, except for the nuclei observed here and there 

 on their course, are homogeneous and vary very considerably in thickness 

 with the fibres which they cover, being 0"5 to 2 /x in the extraordinarily 

 thick fibres (100 to 150 /j.) and discernible with difficulty in those which are 

 very narrow (2 to 5 /x).* This sheath is, therefore, morphologically different 

 from the neurilemma of vertebrate nerve fibres, but it certainly exercises the 

 functions of that structure. 



When the teased-out fresh fibres of the ganglionic chain of the lobster or 

 crayfish are treated with the acid nitrate of silver solution for 24 hours, the 

 reagent penetrates the sheaths of the larger fibres only slowly, and gives 

 to their contents a diffuse chloride reaction, usually a feeble one, but 

 varying according to the degree of penetration. The penetration of the 

 smaller fibres is always more pronounced, owing to the greater tenuity of 

 the membrane, and, in consequence, one gets reactions, like that represented 

 in fig. 9, a, limited to the contents in which, besides the diffused condition of 

 the chloride precipitate, there is also a finely granular deposit of the latter. 



When the reagent, instead of entering the nerve fibre through the intact 

 sheath, gains access to the axial contents by the open ends of a torn or 

 interrupted membrane, the result is a Frommann striation. This has been 

 seen by us only very rarely in the case of the larger fibres, but frequently 

 in the smaller ones, long segments of which exhibited the peculiarity. The 

 striation found was typical (fig. 9, h), and was often seen in fibres immediately 

 adjacent to others whose sheaths were intact and in which the reaction 

 was a uniformly diffuse one. This is, we believe, the first instance observed 

 of the production of the striae in the nerve fibres of invertebrates, and the 

 failure of Jakimovitch and others to obtain such stria? in their preparations 

 may have been due to the possibility that they did not tease out their 

 preparations so as to allow the reagent to penetrate sufficiently the parts, or 

 that they did not make sufficiently extensive observations on their material. 



* Emil Yung, "Kechercbes sur la Structure Intime et les Fonctions du Systerue 

 Nerveux Central ehez les Crustaees Decapodes," 'Arch, de Zool. Exper., ; vol. 7, p. 401, 

 1878. 



