PARAFFIN METHOD 93 



Petrunkevitch [Science, Ixxvii, 1933, p. 117) uses phenol 

 directly with the fixative and recommends the following : — 



Stock solution A : 



Distilled water .... 



Nitric acid, c.p. .... 



Cupric nitrate, c.p. .... 



Stock solution B : 



80 per cent, alcohol .... 



Phenol, crystals, c.p. 



Ether ...... 



Take 1 part of solution A and 3 parts of solution B. Fix 

 immediately as this mixture does not keep well. Twelve to 

 twenty-four hours is usually sufficient, but in no case should it 

 exceed forty-eight hours. Wash in several changes of 70 per cent, 

 alcohol. 



Slifer and King [Science, Ixviii, 1933, p. 366) have foimd that 

 tissue fixed by some other method and subsequently treated with 

 a 4 per cent, solution of phenol dissolved in 80 per cent, alcohol 

 very effectively softens the yolk of a grasshopper's egg so that it 

 may be sectioned with very little difficulty. 



174. Ribbon Section-cutting. If a series of paraffin sections be 

 cut in succession and not removed from the knife one by one as 

 cut, but allowed to lie undisturbed on the blade, it not infre- 

 quently happens that they adhere to one another by the edges 

 so as to form a chain or ribbon which may be taken up and trans- 

 ferred to a slide without breaking up, thus greatly lightening the 

 labour of mounting a series. For the production of a ribbon, the 

 paraffin must be of a melting-point having the right relation to the 

 temperature of the laboratory, see § 169. Secondly, the knife 

 should he set square. Thirdly, the block of paraffin should be 

 trimmed so as to present a straight edge parallel to the knife- 

 edge ; and the opposite edge should also be parallel to this. It 

 is by no means necessary to have recourse to special mechanical 

 contrivances, as in the so-called ribbon microtomes ; the Thoma 

 microtome is sufficient. But the automatic microtomes, and 

 amongst them the Cambridge Rocking Microtome and the Minot, 

 are certainly most advantageous for this purpose 



If the paraffin is very hard, it is necessary for sections of 10 /n, 

 and advisable for thinner ones, to coat the block with softer paraffin. 

 To do this, take paraffin of about 40° C. melting-point, melt it, 

 heat it to about 80° on the water-bath, dip the block into it 

 for an instant, and rapidly turn it over so that the fluid paraffin 

 may run down away from the top part as much as possible. 

 Allow it to cool, and pare away again the soft paraffin from the 

 two sides that are not to be arranged parallel to the knife. Or, 



