THE MICROSCOPE AND MICROSCOPIC METHODS 57 



they may be cut after freezing. Bacteria stain admirably in 

 frozen sections. For routine work collodion imbedding will be 

 found as convenient a process as any. Paraffin imbedding gives 

 the thinnest sections. 



A microtome consists of a heavy, sliding knife-carrier, which 

 moves with great precision on a level, and of a device for elevating 

 the object which is to be cut, any desired distance after each ex- 

 cursion of the knife. The thickness of the section will be the 



FIG. 27. Schanze microtome. 



distance which the object is elevated. The knife is kept wet 

 with alcohol during the cutting of collodion sections, otherwise 

 it is left dry. The microtome is usually provided with a special 

 form of knife. A razor will serve nearly as well, after having 

 had the lower side ground flat. If a razor is used, a special form 

 of razor-holder must be attached to the microtome to receive the 

 razor. Above all, it is necessary that the knives should be kept 

 in good condition. Only occasionally will they need honing, using 

 a fine water-stone or Belgian hone. The movement in honing 



