THE PARAFFIN PROCESS 221 



more heat would be necessary, as the paraffin melts at about 

 50 C. But the writer has often embedded the blocks by 

 placing them in bottles containing- the paraffin at such a dis- 

 tance from the fire that the paraffin is never completely 

 melted, but always shows a thin solid layer on the surface. 

 To do this it is only necessary to look at the bottle occa- 

 sionally, and move it a little farther 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 soaking- 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 

 laboratory (Fig. 42). 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 



FIG. 42. L-SHAPED MOULDS FOR EMBEDDING IN PARAFFIN. 



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 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 Cath- 

 cart microtome already mentioned. The paraffin block con- 

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



