METALLIC STAINS (IMPREGNATION METHODS). 259 



tissues fixed in his platino-aceto-osmic mixture ( 50). With 

 this modification of the process incomparably better results 

 are obtained. 



. HERMANN'S procedure is as follows : The tissues are put 

 for one or two days into the platino-aceto-osmic mixture, 

 washed thoroughly in water, and hardened in successive 

 alcohols ; after which, to obtain the black reaction, they are 

 put for twelve to eighteen hours into raw pyroligneous acid. 

 This acid ought (Ergebnisse der Anat., ii, 1893, p. 28) to be 

 as raw as possible, and to be of a dark brown colour and 

 evil-smelling. (The stain obtained in this way is not due to 

 a mere reduction of the osmic acid, but also to coloration by 

 the brown pyroligneous acid ; for HERMANN has obtained the 

 same stain with sublimate material, or alcohol material [op. 

 cit., i, 1891 (1892), p. 7]). 



According to my experience, the procedure of HERMANN 

 is not that which gives the best results. I now proceed as 

 follows : 



Either the mixture of HERMANN or the mixture of FLEMMING 

 may be used for fixing. You may leave the tissues therein 

 for twelve or twenty-four hours if you think that this is 

 desirable in the interest of a complete fixation ; but in the 

 interest of the stain alone, half an hour is enough and is 

 preferable. It is not only useless but hurtful to put the 

 preparations into alcohol after fixation, for it is desirable 

 that the tissue should be in as fresh a state as possible on 

 coming into the pyrogallol. In consequence it is not possible 

 to obtain the best results by treating paraffin sections. The 

 tissues are therefore brought in bulk, directly after fixing, 

 into pyrogallol. You may use Hermann's pyroligneous acid 

 if you like, but I consider that a weak solution of pyrogallol 

 is preferable. The tissues may remain in either of these 

 liquids for twenty-four hours, but for small objects an hour 

 or less is sufficient. An alcoholic solution of pyrogallol may 

 be taken if desired, and this way be indicated in certain 

 cases. I have not obtained the reaction with tannin used on 

 chrom-osmium material. 



There is thus obtained a black stain, which is at the same 

 time a plasma stain and a nuclear stain, chromatin being so 

 far stained that it is not necessary to have recourse after- 

 wards to a special chromatin stain. This is one of the best 



