IMBEDDING METHODS (PARAFFIN). 97 



cheap. Dr. Webster writes me that a quality known as " Persian naphtha " 

 is best for fine work, but the comnionjiure naphtha is sufficient for ordinary 

 work. 



FIELD and MAETIX (Zeit.f. wiss. Mik., xi, 1, 1894, p. 10) recommend a 

 light petroleum known as ' ; petroleum-aether." 



Xylol is said by M. HEIDENHAIN (Kern und Protoplasm a, 

 p. 114) to be a cause of shrinkage in cells ; lie employs oil of 

 bergamot. This, according to APATHY (Mikrotechrnk,p. 117), 

 only dissolves very little paraffin. 



For Gueguen's methyl salicylate, see 123a. 



Chloroform mixes well with paraffin, and after evaporation 

 in a paraffin bath (in the manner described in the next para- 

 graph) leaves behind a pure and very homogeneous paraffin, 

 having but little tendency to crystallise. But it 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. Chloroform ought therefore to be reserved for 

 small and easily penetrable objects. Under suitable con- 

 ditions, and properly employed, it is certainly one of the best, 

 if not the very best of these media. 



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

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

 general work the very best clearing agent for paraffin im- 

 bedding. It penetrates extremely 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, I fancy it sometimes improves it by rendering' 

 it less brittle. I do not mean to assert that it is in all cases 

 the best, for for some fine work I think chloroform may give 

 more accurate results. And it may often be indicated to 

 employ the two reagents successively, as recommended by 

 APATHY, see next . 



In some difficult cases anilin oil is indicated (see 



121). 



7 



