56 BACTERIOLOGY 



which requires the use of a water-bath or oven, one to three 

 hours. The xylol must be entirely driven off, and the tissue 

 thoroughly infiltrated. 



(e) Change to fresh paraffin for one hour. 



(/) Finally, place the tissue in a small dish or paper box and 

 pour the melted paraffin about it. Harden as quickly as possible 

 with running water. It is important to fix the piece of tissue 

 in a suitable position, if the position is of importance, before 

 pouring in the melted paraffin. Sections of exquisite thinness 

 may now be cut. The knife need not be wet. Paraffin im- 

 bedding is especially desirable when serial sections are to be made. 



In order to mount the sections, proceed as follows: 



(a) Place the sections on water in a porcelain capsule. 

 Warm slightly, when the sections will flatten nicely. Smear the 

 surface of a slide with a very thin layer of Mayer's glycerin- 

 albumen mixture. Dip the slide under the sections; lift them; 

 and then drain off the water, leaving the sections in their proper 

 positions. Let them dry for some hours in the incubator, and 

 they will be firmly fastened to the slide. 



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. 



(b) Dissolve out the paraffin in one of the numerous solvents 

 (xylol, a few minutes) . 



(c) At this point the xylol should be washed off with absolute 

 alcohol, and then 70 per cent alcohol and finally distilled water. 



(d) The section is stained. 



(e) Dehydrate in absolute alcohol. 

 (/) Clear in xylol. 



(g) Mount in balsam. 



Section Cutting. Cutting is best done with an instrument 

 called a microtome. The tissues may be imbedded in collodion 

 or paraffin; or when they have been hardened with formaldehyde 



