92 PARAFFIN METHOD 



and difficult material should not be left in the higher grades any 

 longer than is necessary for dehydration. Third, some of the 

 clearmg agents render certain types of material both hard and 

 brittle. Fourth, leaving tissues too long in paraffin or over- 

 heatmg them may cause brittleness. Fifth, certain types of 

 tissues, even in the hands of the most experienced worker, are 

 always hard and brittle when treated by ordinary methods.' In 

 these cases one should try one of the methods which are described 

 below : — ■ 



173. A. Johnston's Rubber Paraffin. {Jour. Ajml. Micr vi 

 1903, p. 2662). ■' ' 



Crude india-rubber, cut in small pieces . 1 part by weight. 

 Paraffin, melted and tinged an amber 



colour with asphalt . . . .99 parts. 



Heat to 100° C. twenty-four to forty-eight hours. If a lower 

 temperature is used treat the paraffin for a week or ten days. 

 Then pour off the supernatant fluid and cool at once. Use 

 ordinary paraffin, but note that if you allow rubber paraffin 

 to stand melted in the oven for a long time it tends to 

 decompose. 



Johnston's rubber paraffin is, perhaps, the most valuable aid 

 we have for sectioning tissues which would be hard and brittle in 

 ordinary paraffin. 



B. The N- Butyl Alcohol Method. This method is useful when 

 one wishes to avoid the hardening effect of ethyl alcohol and such 

 a clearing agent as xylol. (See § 127.) 



N-butyl alcohol is only slightly soluble in water, but mixes 

 readily with the higher grades of ethyl alcohol and also with 

 paraffin, so that no separate clearing agent is needed. 



The N-butyl alcohol method was originally used for making 

 sections of woody tissues which were too hard for ordinary methods 

 but is now recommended for making sections of lightly chitinised 

 msects, and promises to be a very useful adjunct for difficult 

 material. For details refer to § 127, p. 63. 



C. Dioxan Method. This method also avoids the use of ethyl 

 alcohol and benzol or xylol. Refer to § 130, p. 64. 



D. Hardening Wax by Ceresin Method. This method enables 

 one to harden the wax and to get something approaching the 

 celloidin-wax method. It has been recently used a good deal. 

 See § 177. 



E. Double Imbedding in Paraffin Wax and Celloidin. See 



§190. 



F. Treatment with Phenol. Phenol has long been known to 

 impart to tissues an elastic texture and recently several methods 

 have been developed which employ this agent to soften tissues 

 which would otherwise be hard and brittle on sectioning. 



