THE PARAFFIN PROCESS 187 



completely melted, but always shows a thin solid layer on the 

 surface. To do this it is only necessary to look at the bottle 

 occasionally, and move it a little further from the fire if the 

 paraffin is completely melted, and vice versa. The process may 

 be stopped at night without any harm resulting, and if the soakmg 

 only continues for a few hours at a time it is of no consequence so 

 long as the total period is made up. 



Casting the Blocks. — Special metal moulds are used in the labora- 

 tory (Fig. 37). A pill-box will do quite well. A small amount of 

 melted paraffin is poured into the box, and the piece of tissue is 

 taken from the bottle containing the melted paraffin with a pair of 

 forceps (previously warmed, so as to prevent the paraffin from 

 setting upon the points), and placed in the paraffin in the pill-box. 

 It is necessary to see that the surface from which sections are to 

 be cut should be placed downwards. The box is then filled up 

 with melted paraffin, and placed in a cool place or surrounded with 



Fig, 37. — L-sH.^PED Moulds for embedding c P.^raffin. 



water. The moment a firm film has formed over the surface the 

 whole is plunged in cold water to hasten the setting of the paraffin ; 

 the more rapidly this takes place the better will the block cut. 

 When the paraffin mass has hardened completely throughout, it 

 is trimmed into shape, taking care that the edges of the surface 

 which is to be cut are accurately parallel. 



Cutting the Sections. — For cutting sections in paraffin no 

 microtome can be compared with the Cambridge Rocker, but 

 very excellent results can be obtained by the use of the 

 Cathcart microtome already mentioned. The paraffin block 

 containing the piece of tissue is mounted on the freezing-plate 

 of the microtome (which must be heated, and the lower surface 

 of the block pressed upon it), and the sections cut in the manner 

 described ; a very sharp knife is essential, and the stroke must be 

 quicker and sharper than is the case when frozen sections are 

 being cut. In another form of the microtome a special mner 



