SECTIONING 279 



of the sections to be cut. The strokes of the knife should be smooth 

 and rai)id. The knife should have been correctly sharpened to 

 secure f^ood sections. Sections of from 10 to 30 microns are usually 

 cut, but with practice thinner ones may be obtained. Single 

 sections are obtained by this method, and these must be transferred 

 with a camel's-hair brush as they are cut to a dish containing 70 per 

 cent alcohol. 



Mounting Paraffin Sections. After paraffin sections have been 

 cut and transferred to a paper box, the next step is to attach them 

 to slides. The sections as they come from the microtome are 

 usually slightly compressed or wrinkled, due to the pressure as they 

 cross the knife. This must be remedied when the sections are 

 attached to the slides. In the first place the slides must be thor- 

 oughly clean so that no dirt or grease particles are on their surfaces. 

 They can be cleaned by boiling in soap and water, thoroughly rinsed 

 in water, then rinsed in 95 per cent alcohol, and dried with a clean 

 cloth free from lint or dust. Next, the sections must be made to 

 adhere to the slide to permit the subsequent steps of the staining 

 technique. A solution of equal parts of carefidly strained egg- 

 white and glycerin is used as an adhesive. A small amount of 

 thymol or methyl salicylate added to the adhesive mixture 

 prevents disintegration by bacterial action. A common method 

 of applying the egg-albumen adhesive is as follows: A small 

 drop about the size of the head of a pin is placed in the center 

 of one surface of the slide, and this drop is carefully smeared over 

 the surface with the ball of the little finger that has been thoroughly 

 washed. A drop or two of distilled water is then added to the 

 surface. Then a small piece of ril)bon containing one or two sec- 

 tions of the tissue is cut from the long ribbon with a scalpel and 

 transferred to the water over the egg albumen on the slide. It is 

 advisable to use water that has been boiled (and cooled) to avoid 

 bubbles gathering between the slide and the sections. The ribbon 

 piece should be arranged parallel with the length of the slide. Two 

 or even three small ribbon pieces may be arranged alongside each 

 other. The same surface that is upward when the ribbon comes 

 from the microtome should be upward on the slide. The under 

 side is more shiny than the upper. After the ribbon pieces have 

 been arranged, the slide can then be transferred to a warming table 

 (Fig. 166), the surface of which is kept at a temj^erature of about 

 45° C. or a little less. More water can be added to float the sections 

 but not enough to run off the slide. The gentle heat warms the 



