Accessory Apparatus 251 



we advise the beginner to avoid, for, owing to their awkward 

 handles, they are rather difficult to hold in sharpening. 



Each of the above knives, with the exception of Weikert's, 

 is made in three degrees of concavity or hollow-grinding to 

 their upper surface. Most microtome knives have their 

 under surface plane. 



Pig. 70.— Thoma's Microtome Knife with Curved Handle. 



In Fig. 71, A is the most hollow-ground, or thin-edged, 

 as it is sometimes termed ; it is most serviceable for very 

 delicate objects and for the wet-cutting process. C repre- 

 sents the least hollow-ground, or thick-edged ; it is especially 

 valuable for hard objects, or for the ice-embedding process. 

 B is intermediate, and is especially suitable for the paraffin 

 method, and is the most useful sectional shape of all. 



Knives Necessary. — A beginner, starting with a sledge 

 microtome (that is, Eivet or Schanze type) having a tram- 



a b c 



Fig. 71. — Three Forms of Microtome Knives in Sectional View. 



way 25 centimetres long, should have, at least, as follows : 

 One Henking's knife — blade, 6 centimetres ; handle, 9 centi- 

 metres ; grinding B. One Henking's pattern — blade, 6 centi- 

 metres ; handle, 9 centimetres ; grinding C. One Jung's 

 pattern — blade, 16 centimetres, with screw handle ; grind- 

 ing B. 



A case in which to keep the knives is an absolute 

 necessity. 



