CELLOIDIN 105 



adding a small proportion of medicinal paraffin to 45° C. wax. 

 The block is finally infiltrated with 45° C. wax. Care must be 

 taken with the first infiltration to prevent shrinkage of the 

 celloidin block by too rapid removal of the cleanng lluid. Small 

 blocks can be transferred direct from chloroform to the low 

 melting-point wax. 



191. Rapid Celloidin Imbedding. In certain special mstances 

 with very small pieces of material a much more rapid imbeddmg 

 may be obtained by Gilson's process (1892). The material, after 

 dehydration and soaking in the celloidin solvent, is placed m a 

 thin celloidin solution in a test-tube which is dipped m a bath of 

 melted paraftin. The celloidin is allowed to boil until it becomes 

 viscous. The tissue is then cast in the concentrated celloidm or 

 turned out on to a block of hardened celloidin and the whole 

 hardened in chloroform or a mixture of chloroform and cedarwood 

 oil for one to several hours. The hardened block is then cleared 

 in cedarwood oil, fixed to a block holder and cut with a knife 

 moistened with the oil. 



192. Storage of Celloidin Blocks. Celloidin blocks are usually 

 stored in 70 per cent, alcohol or in a mixture of alcohol and 

 glycerin. The blocks infiltrated with cedarwood oil may be 

 kept in air-tight containers, see Walls {Stain Tech., xi, 1936, p. 89). 

 It is best to cast the paraffin infiltrated blocks in a fresh coating 

 of wax to prevent evaporation of any volatile reagents which may 

 have remained in the celloidin as the result of incomplete infiltra- 

 tion. This applies particularly when the surface of the tissue has 

 been exposed in cutting. 



Some histologists prefer to leave the decalcification ot bone 

 and teeth until the material is imbedded in celloidin and trans- 

 ferred to alcohol. A radiograph can be taken of the celloidm block 

 beforehand to indicate the distribution and density of the 

 calcification and then the block is immersed in the decalcifying 

 fluid By taking further radiographs at intervals the material 

 need not be left in the acid for any longer period than is required 

 to obtain complete decalcification. In this way the harmful effects 

 of prolonged exposure of tissues to acids and the objectionable 

 methods of prodding the tissue with a needle to gauge the progress 

 of the decalcification, may be avoided ; see Hallpike {Journ. Path, 

 and Bact., xxxviii, 1934, p. 249). 



193. Mounting and Trimming for Section Cuttmg. Block 

 holders for celloidin work are now usually made from fibre or hard 

 wood It is convenient to have a large number of them prepared 

 so that mounted blocks may be stored, pending further section 

 cutting, without detaching them from their holders. The celloidm 

 block is easily attached to a holder by cutting a plane surface on 

 the base of the block and brushing the surface and that of the 

 holder with alcohol-ether. A drop of 16 per cent, celloidin is 



