82 r IIAITK ii vi i r. 



Xylol is said by M. HEIDENHAIN (Kern und Protoplaema, 

 p. 114) to be a cause of shrinkage in cells. So it is, if you 

 use it to de-alcoholise the specimens. But used after oil of 

 cedar, or the like, it is very good, as it is one of the best of 

 solvents of paraffin. 



Chloroform is deficient in penetrating power, so that it 

 requires an excessive length of time for clearing objects of 

 any size ; and it must be. very thoroughly got rid of by 

 evaporation in the paraffin bath, or by successive baths 

 of paraffin, as if the least trace of it remains in the paraffin 

 used for cutting it will make it soft. The process of removal 

 requires a very long time, in some cases days. It ought 

 therefore to be reserved for small and easily penetrable 

 objects. 



Naphtha has been recommended by WEBSTER (Jousn. An at. <nnl 

 PhysioL, xxv, 1891, p. 278). 



FIELD and MARTIN (Zeit. wiss. Mile., xi, 1894, p. 10) recommend a 

 light petroleum known as " petroleum -sother." It is highly volatile. 

 and thus a cause of shrinkage. 



Sulphide of carbon has been recommended by HEIDENHAIN (Zeit. 

 wiss. Mile., xviii, 1901, p. 166) as being a very powerful solvent of 

 paraffin. Most workers have found it to ]>e much too disagreeable and 

 dangerous a reagent for ordinary work, and not necessary even for 

 delicate work. 



Carbon tetrachloride has l>eeii recommended by PLECNIK (op. cit., \i\. 

 1903, p. 328) and PRANTER (ibid., p. 329) on the ground of not dissolving 

 out osmium-blackened fats. 



MAYER finds it no letter than benzol. 



As a general thesis, the best of all these are cedar oil, 

 benzol, and chloroform. 



Cedar-wood oil is, according to my continued experience, 

 for the reasons stated by me in Zool. Ariz., 1885, p. 563, for 

 general work the very best clearing agent for paraffin im- 

 bedding. It penetrates rapidly, preserves delicate structure 

 better than any clearing agent known to me, does not make 

 tissues brittle, even though they may be kept for weeks or 

 months in it, and has the great advantage that if it be not 

 entirely removed from the tissues in the paraffin bath it will 

 not seriously impair the cutting consistency of the mass; 

 indeed, 1 fancy it sometimes improves it, by rendering it less 

 brittle, 



