40 MANUAL OF BACTERIOLOGY. 



(/) Clear in xylol. 

 (g) Mount in balsam. 



GLYCERIN-ALBUMEN MIXTURE (MAYER). 



Equal parts of white of egg and glycerin are thoroughly mixed, and then 

 filtered. 'Add a little gum-camphor to preserve. 



Section Cutting. Cutting is best done with an instrument 

 called a microtome. The tissues may be imbedded in collo- 

 dion or paraffin; or when they have been hardened with for- 

 maldehyde they may be cut after freezing. Bacteria stain ad- 

 mirably in such 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 excursion of the knife. The thickness of the section 

 will be the 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 micro- 

 tome 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. 

 Preferably the knife should not be honed directly on the stone 

 itself but on a piece of clean plate glass, on which the stone is 

 first rubbed with water. By this means the entire cutting 

 edge is sharpened in one plane. The movement in honing 

 should be from heel to toe, and toward the cutting edge, always 

 placing the back of the knife next the hone when turning. The 

 knife should be stropped frequently. The leather of the strop 

 should be glued to a strip of wood to make a flat surface. The 



