68 



Animal Micrology 



sharpened blade of a carpenter's plane is the best instrument for 

 cutting. It must be frequently stropped. 



The blade should be mounted in a short, broad handle, which may be 

 grasped easily and firmly with one hand. In cutting, the bevel edge of 

 the knife should set squarely on the glass ways of the microtome so that 

 the handle of the knife is inclined toward the operator at about an angle 

 of 45 degrees from the perpendicular. The hand guiding the knife should 

 be firmly supported against the chest while pressing the cutting edge 

 steadily against the glass ways of the 

 microtome. The cutting stroke is 

 made by bending the body forward 

 from the waist and thus forcing the 

 blade squarely across the surface of 

 the tissue. 



The blade must be kept cold to 

 prevent sections from sticking to 

 it. If the sections fly off or roll, 

 the tissue is probably frozen too 

 hard. The same defect may arise 

 if there is insufficient syrup in the 

 gum with which the tissue has 

 been saturated. To correct, let the 

 tissue thaw a little, and if still at 

 fault, soak it again in a mixture 

 which contains a greater propor- 

 tion of syrup.' Work rapidly, so 

 as to cut sections in quick succes- 

 sion. Several sections may be 

 allowed to collect on the blade 

 before they need be removed. 



7. Transfer the sections to dis- 

 tilled water. The water should be changed several times to dis- 

 solve out the gum. Reserve a few sections in water for later use 

 (step 11). 



8. Immerse a few of the sections for 10 to 30 minutes in 

 Delafield's hematoxylin, then wash them in several changes of 

 tap water. 



FIG. 33. Bardeen Carbon-Dioxide Freez- 

 ing Microtome. 



The freezing chamber contains a 

 spiral passage through which the expand- 

 ing carbon-dioxide passes, securing the 

 maximum freezing power. The knife 

 slides on glass guides. The finest feed is 

 twenty microns. 



