46 Botanical Microtechnique 



6.3 C) . Move the knife carrier forward and the tissue carrier down- 

 ward until the material almost touches the knife-edge in its downward 

 travel. Check the setting of the thickness gauge. Make sine that the 

 wedge-like cutting edge is tilted to have proper clearance on the 

 return stroke (Fig. 6.3 A, B) . This angle must be determined by 

 trial. Inadequate clearance residts in compression of the tissues by 

 the forward flat face of the knife or b\ the edge of the razor-blade 



Fig. G..S— Orieiitaiion of tissues in relation to the knife: A, knife with the gnninil 

 cutting wedge and the hollow grind exaggerated to sliow necessary clearances of 

 angles 2 and 3 and faces 1 and 4: B. razor-blade holder, sliowing declination neces- 

 sary to clear edge (5) of the clanip; C, lop view of niounting l)lock, jKirallin block, 



and knife-edge. 



holder (Fig. 6.3 A, B) . Too much angle results in a s(raj)ing action 

 rather than a chisel action of the knife-edoc. 



Having checked the above points, tinn the operating -wheel slowl\, 

 and at the top of each upstroke, turn the hand crank of the feed 

 mechanism one revolution, iiniil tadi downstroke removes a complete 

 slice. Clean the knife-edge by drawing the tluiinl) ;iiul forefinger along 

 the front and back faces of the knife, and proceed with ihe i ibboning. 

 Operate the wheel at such speed that there is no marked compression 

 of each slice and successive slices adhere to form a straight ribbon. 

 Note that an exjx'rienced worker does not turn the wheel at miiroiin 

 velocity dining a re\olution. As the tissue apj^roaches the knife, a 

 sna[) of the wrist increases velocity considerably at the moment of 

 contact between the tissue and the knife. Ihis speed promotes clean 



