178 Prof. A. B. Macallum and Miss M. L. Menten. [July 24, 



or five hours many fibres show the typical Frommann striation to extend over 

 considerable extents of their axons. There are, as already pointed out, 

 in such preparations fibres which show very considerable alterations in the 

 disposition of the chlorides, and this is a serious objection to the employment 

 of a solution of the reagent in which the nitric acid is so highly concentrated. 

 If the reagent of this strength diffuses into the fibre properly, the result should 

 be, and usually is, a striking demonstration of Frommann' s lines over a 

 considerable extent of many of the affected axons. On che other hand, a 

 diffuse silver reaction in the axons of fibres of the same preparation is, in the 

 majority of cases at least, the result of the failure of the reagent to penetrate 

 normally, and the diffuse reaction itself is very often an indication of an 

 artificially altered distribution of the chlorides of the axon. 



It is otherwise with nerve fibres which, like those of the spinal cord or of 

 the optic nerve, are unprovided with neurilemmal sheaths, for these may, and 

 oftenest do, show a uniformly diffused reaction for chloride of silver extending 

 over long stretches of the axons and wholly confined to them. These axons 

 are not swollen or altered in any morphological aspect, and everything 

 indicates that the reaction they give is not, as in the case of fibres provided 

 with neurilemmata, due to imperfect penetration, but rather to rapid diffusion 

 into the axons and the immediate precipitation of the chlorides before these 

 can be redistributed. 



Such preparations may be obtained by pressing portions of the spinal cord 

 between two slides to very thin layers, and treating them at once and for 

 24 hours with either the ordinary reagent or that in which the acid constituent 

 is of 10-per-cent. strength. 



Many of the fibres in such cases are easily and completely interrupted at 

 points by the pressure to which they are subjected, and in consequence one 

 may find amongst them portions of axons which reveal a Frommann 

 striation as pronounced as any that may be found in fibres provided wich 

 neurilemmata, and these lie side by side with greater lengths of uninterrupted 

 nerve fibres which show a diffuse silver reaction confined to unswollen and 

 normal axons. 



The explanation for the differences in the silver reaction between fibres 

 from the spinal cord on the one hand and those from ordinary nerves on 

 the other must be referred to the absence or presence of the neurilemma. 

 Ordinary nerve fibres are not readily penetrated by the silver reagent 

 except at the nodes, and even when the nitric acid in the reagent is of 

 10-per-cent. strength, the point of entrance is still, in great part, if not 

 wholly, the node, whereas in preparations from the spinal cord, the 

 medullated fibres of which have no neurilemmal sheaths, the noteworthy 



