18 MICROSCOPY. 



5, Sectioning. This consists in cutting thin sections of the ob- 

 ject to be examined. It is accomplished by the use of a razor, or mi- 

 crotome knife, which may be used free-hand or with a microtome. 

 To cut paraffin sections, first pare the block to the right size and then 

 fasten it in the clamp of the microtome. The paraffin should be 

 kept at the right temperature. This may be accomplished by using 

 cold or hot water, applying it with a camelVhair brush, or with the 

 heat of the hand or a flame. The knife should be drawn at a slight 

 angle. If sections curl, they may be placed upon the surface of 

 moderately warm water to flatten them. Curling may be prevented 

 by holding the sections in place with a cameFs-hair brush as they 

 are cut. 



Celloidin sections are cut in the same way, with the exception 

 that the knife and celloidin block must be kept constantly flooded 

 with seventy-five per cent alcohol. The sections when cut may be 

 removed to a vessel containing seventy-five per cent alcohol, and 

 there kept indefinitely. 



6. Fixation. This consists in attaching sections to the slide. 

 Paraffin sections may be affixed with collodion mixture, or with egg- 

 albumen and glycerine. To affix with collodion, make a thin layer 

 with camelVhair brush upon the slide. Then apply the section, 

 flattening it out with finger or brush; now apply the heat of a spirit 

 or Bunsen flame until the paraffin melts, being careful to avoid 

 excessive heating, such as would injure the tissue. To affix with 

 egg-albumen and glycerine, a thin coating is made with a camel's- 

 hair brush, and the section is then transferred to the center of the 

 slide, care being taken to flatten it out with finger or brush. Heat 

 is then applied to coagulate the albumen. To avoid overheating, 

 the slide should be frequently applied to the surface of the hand. 

 When the paraffin becomes thoroughly melted the section is usually 

 properly affixed. 



If desired to affix celloidin sections, a drop of ether may be ap- 

 plied to each section after placing it in the desired position, or they 

 may be affixed with the collodion and clove-oil mixture in the fol- 

 lowing manner : Apply a thin layer of collodion mixture to center of 

 slide ; when the collodion is dry apply the section, together with the 

 thin piece of paper upon which it has been placed, and press upon 



