80 PARAFFIN METHOD 



Naphtha has been recommended by Webster {Journ. Anat. and 

 Physiol., XXV, 1891, p. 278). 



Field and IVLvrtin (Zeit. wiss. Mik., xi, 1894, p, 10) recommend a 

 light petrolemn known as " petrolemn-aether." It is highly volatile, 

 and thus a cause of shrinkage. 



Sulphide of carbon has been recommended by Heidenhain {Zeit. 

 zviss. Mik., xviii, 1901, p. 166) as being a very powerful solvent of 

 paraffin. Most workers have found it to be much too disagreeable and 

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

 delicate work. See under " Teeth " and " Chitin." 



Carbon tetrachloride has been recommended by Plecnik (op. cit., xix, 

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

 out osmimii-blackened fats. 



Mayer finds it no better than benzol. 



Cedanvood oil is, according to continued experience, for the 

 reasons stated by Lee in Zool. Anz., 1885, p. 563, for general 

 work the very best clearing agent for paraffin imbedding. It 

 penetrates rapidly, preserves delicate structure better than any 

 clearing agent known, 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 con- 

 sistency of the mass ; indeed, it sometimes improves it by rendering 

 it less brittle. As has been mentioned above (§ 131), methyl 

 benzoate-benzol is now being used a good deal instead of the 

 cedar oil method. It should be noted that care must be taken 

 to buy a high quality of cedar oil. 



Xylol certainly causes shrinkage when used alone. It is 

 excellent practice to clear first in cedarwood oil and then wash 

 out in benzol or xylol, or to use the methyl benzoate-benzol 

 method (§131). 



159. The Paraffin Bath, The objects having been duly 

 saturated with a solvent, the next step is to substitute melted 

 paraffin for the saturating medium. 



Some authors lay great stress on the necessity of making the 

 passage from the saturating agent to the paraffin as gradual as 

 possible, by means of successive baths of mixtures of solvent and 

 paraffin kept melted at a low temperature, say 35° C. With 

 oil of cedar, at all events, this is not necessary. We simply put 

 the objects into melted paraffin kept just at its melting-point, 

 and keep them there till they are thoroughly saturated ; the 

 paraffin being changed once or twice for fresh only if the objects 

 are sufficiently voluminous to have brought over with them a 

 notable quantity of clearing agent. If the objects have been 

 for a very long time — months or years — in the cedar oil so that 

 this has become thick Lee removes it partially or entirely by 

 soaking in xylol (thirty minutes to several hours) before putting 

 into the paraffin. But with fresh oil of cedar he finds no advantage 

 in doing so. (See, however, § 808.) 



