THE PARAFFIN PROCESS 1 69 



In the Cambridge Rocker and in some other forms of micro- 

 tomes the sections adhere to one another at the edges, and form 

 long ribbons as they are cut. In the Cathcart microtome this is 

 not the case, and each section must be dealt with separately ; it 

 is to be removed carefully from the knife-blade with a camel's- 

 hair brush or a finely pointed pair of forceps, and placed upon 

 the surface of a bowl of water, just hot enough to warm the 

 paraffin without melting it. When this is done the sections will 

 spread out and lose all the creases, and are then ready to be 

 mounted on slides or cover-glasses. 



It often happens that the sections roll up on the knife. In this 

 case they must be placed on the surface of cold water, and an 

 attempt made to straighten them out by careful brushing with a 

 camel's-hair brush ; when fairly flat they are to be lifted up on 

 a slide or piece of paper (dipped into the water and insinuated 

 below them), and transferred to the hot water as before. But 

 the rolling of the sections may often be prevented 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 excess of water is now to be removed by a piece of blotting 

 or filter paper, and the slide placed in the warm incubator 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 



