IMBEDDING METHODS ( PARAFFIN). 113 



cohere. It is by no means necessary for this purpose to have 

 recourse to special mechanical contrivances, as in the so-called 

 ribbon microtomes. The Thoma microtome well flooded with 

 oil is sufficient. But the automatic microtomes, and amongst 

 them the Cambridge Rocking Microtome, the Reinhold-Giltay, 

 and the Minot, are certainly most advantageous for this pur- 

 pose. 



Various plans, such as coating the edges of the paraffin with softer 

 paraffin, or with Canada balsam, or the employment of specially prepared 

 paraffin, have been recommended, with the idea that they help the sections 

 to stick. I find that none of these devices are necessary. For the prepared 

 paraffin of Spee, see below, 142. 



MAYER, however (Grundzuge, p. 86), remarks hereon, that though 

 coating with a softer paraffin is not necessary when soft paraffin is taken 

 for imbedding, yet if a paraffin of 55 to 60 melting-point is used for 

 imbedding, it is absolutely necessary to coat it with softer, for sections of 

 10 fi thickness, and at least advisable for thinner ones. To coat the block, 

 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. Large blocks 

 may have two coatings given them. 



It sometimes, though rarely, happens that the ribbon becomes electrified 

 during the cutting, and twists and curls about in the air in a most fantastic 

 and undesirable manner. It may be got flat by warming slightly ; but 

 there is no known means of preventing the electrification. 



138. Section-flattening 1 (very important). The sections 

 having been obtained may be cleared and mounted at once 

 if they are quite perfect, that is, neither rolled nor creased 

 nor compressed. But should they in the least degree show 

 any of these defects, they must first be unrolled or smoothed, 

 or expanded to their proper dimensions. It is most impor- 

 tant not to neglect this point, as is often done in the case 

 of sections that are neither rolled nor crumpled, but are 

 compressed, as shown by their being of smaller area than 

 the block from which they have been cut. 



The most efficacious plan for flattening and expanding 

 sections is the combined treatment with fluid and heat 

 (GASKELL, Quart. Journ. Mic. Sci., xxxi, 1890, p. 382 ; M. 

 DUVAL, Journ. de I'Anat. et de la Physiol., 1891, p. 26 ; 

 HENNEGUY,, ibid., 1891, p. 398 ; GULLAND, Journ. of Anat. 

 and Physiol., 1891, p. 56 ; and others). The sections' are 



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