DEHYDRATION 65 



with Bouin, Carnoy, Formol, or witli fixatives which are washed 

 out in water, as for instance, chrome ones. Corrosive sublimate 

 fixed pieces must go through alcoliols as usual to 70 per cent, and 

 iodine, but may then be placed in dioxan. In general, pieces 

 dehydrate in fresh dioxan in twenty-four hours, and should be 

 changed several times. Smaller pieces can be dehydrated very 

 rapidly. We have used dioxan very successfully for imbedding 

 pancreas by bringing the material into equal parts of dioxan and 

 water, pure dioxan, equal parts of dioxan and wax, and so on. 

 We believe this is better than dropping the pieces into pure dioxan. 

 The possibilities of dioxan have not yet been fully investigated.* 

 After use, the dioxan can be collected and dehydrated by placing 

 a bag of calcium chloride in the bottle. Some workers use a wide- 

 mouthed glass-stoppered jar with a copper gauze layer near the 

 bottom and calcium chloride below the gauze. Pieces to be 

 dehydrated are dropped on to the gauze and recovered with forceps 

 after over-night immersion. 



131. Methyl benzoate (CgHs . COO . CHg) B.P., 198-6" C. 

 S.G. 1-0942. Refractive index 1-517. This substance has been 

 used for many years on the Continent, but only recently has it 

 become popular in British and American laboratories. It is said 

 to remove the last traces of water left after dehydrating in ethyl 

 alcohol, and by clearing the blocks or embryos, enables one to see 

 how successfully dehydration has been carried out. Since its 

 refractive index is very close to that of cedarwood oil, it is now 

 used as immersion oil, with the advantage that it need not be 

 wiped off, as it evaporates. 



It is used as follows in imbedding. From absolute alcohol the 

 piece of tissue is passed through two changes of pure methyl 

 benzoate, twelve to twenty-four hours in each, according to size 

 of piece. The material will clear beautifully. Then transfer to 

 benzol (two changes for twenty to thirty minutes) and through to 

 a mixture of wax and benzol. (Refer also to § 177.) 



Some people go from 96 per cent, ethyl alcohol to methyl 

 benzoate for objects which would harden too much in absolute 

 alcohol. Material does not harden in the benzoate. 



Peteefi {Zeit.f. wiss. Mikr., 38) has a method of passing pieces 

 of tissue dehydrated in alcohol into three changes of 1 per cent, 

 celloidin in methyl benzoate, then in benzol, and benzol wax 

 mixture. Methyl benzoate is not a cheap substance, and for most 

 purposes it is sufficient to see that the absolute alcohol is all right. 



132. Methylal Method (L. Genevois, J. Dufkenoy, Sci., October, 

 1935). Methylal or Formal is methylen dimethyl ether CH2(0 . CH3)2, 

 B.P. 42° C, dissolves 3 parts water. Genevois has suggested a method 

 favourably reported by Dufrenoy. Material is fixed and then brought 



* It has recently been suggested to use dioxan as the basis of fixatives 

 just as alcohol is used in Carnoy, see § G72. 



VADE-MECUM. 3 



