THE PARAFFIN PROCESS 223 



and insinuated below them), and transferred to the hot water 

 as before. But the rolling of the sections may often be pre- 

 vented by sharpening the knife, by re-embedding the tissues 

 in harder or in softer paraffin according to the weather, or 

 by varying the angle which the knife edge makes with the 

 glass runners of the microtome. These devices can only 

 be learnt by experience. 



When the sections are flattened out on the surface of the 

 hot water, they are ready to be mounted upon slides or cover- 

 glasses : slides are by far the best for beginners. The slides 

 (or cover-glasses) must be perfectly clean, and are best kept 

 in methylated spirit until they are to be used, and the spirit 

 not wiped off. Each slide is then inserted separately into 

 the water in an oblique position, and the section moved until 

 it lies over the centre; the slide is then raised out of the 

 water, and carries the section out with it. 



The exce'ss of water is now to be removed by a piece of 

 blotting- or filter-paper, and the slide placed in a warm incu- 

 bator for a few hours. At the end of this time the sections 

 will adhere by atmospheric pressure (like a boy's leather 

 sucker to a stone), and will not come off in the subsequent 

 processes. If an incubator is not at hand the slides may be 

 placed near the fire (protected from dust), and kept at the 

 body temperature or a little higher for a few hours ; the exact 

 temperature does not matter, and no harm will result if the 

 paraffin melts, provided that the section has previously 

 become dry. 



In the older methods of fixing sections to the slides various 

 forms of cements had to be used, and were a great disadvan- 

 tage. They are quite unnecessary except for sections of the 

 central nervous system ; if these are being dealt with the slide 

 must be coated with a very thin layer of a solution of egg- 

 albumen in water before the section is laid upon it. The 

 process is then exactly the same as before. 



STAINING AND MOUNTING PARAFFIN SECTIONS 



We will suppose that the sections have been cut, flattened 

 out on hot water, and caused to adhere to slides, and shall 

 describe in general terms the steps through which they must 

 be taken before they are ready for examination. In the first 



