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Zbc jfiyation of ll^crve jfibrca b^ fformalin/ 



By Edwin M. Kitchell, M.D. 



WITH the exception of osmic acid, the older fixatives do 

 not preserve without considerable shrinkage of the axis 

 cylinder of the nerve fibre ; therefore, as formalin has, 

 in my hands, given excellent results in the preservation of the 

 axis cylinder, and as its effects on the myelin are also rather inter- 

 esting, I have thought that it might be useful to publish a note on 

 the subject. 



The tissues used in my experiments were pieces of the sciatic 

 nerves of the dog and of the rabbit, cut through their entire 

 thickness. Even with pieces of tissue of this size, formalin pene- 

 trates and fixes the fibres throughout the nerve. I used one, two, 

 ten, twenty-five, fifty, and a hundred per cent, of the commercial 

 solution.! 



In the specimens treated with one and two per cent, formalin, 

 the axis cylinder and myelin were both shrunken, as they would 

 be by alcohol, for example. Ten per cent, causes less shrinkage 

 than two per cent, but is still unsatisfactory. In the specimens 

 fixed in twenty-five, fifty, and a hundred per cent, the axis cylin- 

 der remains entirely or almost unbroken in the majority of the 

 fibres. The results were rather better with formalin of full 

 strength. The diameter of the unshrunken axis cylinders, under 

 these circumstances, is about 0*5 to o*8 of that of the entire fibre. 



I tried staining the nerve fibres fixed in 'formalin with acid 

 fuchsine, eosine, and other aniline dyes ; also Gage's haematoxylin, 

 (over-staining). All these colour the connective tissue strongly 

 while the unshrunken axis cylinder is but lightly stained. I 

 thought Gage's hsematoxylin rather the best. Axis cylinders, on 

 the other hand, which are considerably shrunken, are readily 

 stained by these dyes. This may, perhaps, be explained by the 

 concentration of the material taking the stain in a smaller space, 

 which is the case when the axis cylinder is shrunken. 



Transverse sections of the fibres in twenty-five to one hundred 



* From The New York Medical Journal, July 20th, 1895. 

 t This is a forty per cent, aqueous solution of formaldehyde. 



