TREATMENT OF SECTIONS 57 



sufficiently firmly to the slide to allow staining, etc., 

 without floating off. But if they be thick, or if the stain- 

 ing has to be prolonged, it is preferable to first smear the 

 slide with egg-albumin mixture (egg-white beaten up 

 with a little water, mixed with an equal volume of glycerin, 

 and sodium salicylate, 1 gramme per 100 c.c., added as 

 a preservative, and strained) before picking up the section 

 on it. 



Before staining, the slide with section is immersed in 

 xylol (best in a suitable pot or glass cylinder) for two 

 minutes to dissolve out the paraffin, then in absolute 

 alcohol to remove the xylol. 



The Staining of Bacteria in Sections. The following 

 procedure is common to most methods: The sections are 

 rinsed with distilled water to remove alcohol, and then 

 subjected to the action of the stain for a time varying 

 from a few minutes to several hours. The time is in 

 some cases shortened by warming the staining solution. 

 The sections are next washed, preferably in distilled 

 water, and then in some instances decolorised with a 

 suitable reagent; they are again washed, then counter- 

 stained if necessary. The sections are now dehydrated 

 with alcohol, and then cleared with xylol, cedar oil, or oil 

 of cloves. Xylol or cedar oil is preferable to oil of cloves 

 as a clearing agent, as it has no solvent action on the 

 stains, and the former does not resinify on exposure to 

 the air, and evaporates without leaving a deposit. Great 

 care must be taken to remove all the water from the 

 section by means of absolute alcohol before transferring 

 to the xylol or cedar oil, otherwise the section will not 

 properly clear.* After remaining in the xylol for about 

 two or three minutes, the section, if unattached to the 

 slide, is removed by means of a section-lifter, and then 

 laid out flat by careful manipulation with two small 

 pointed glass rods or needles on a clean glass slide; the 

 excess of clearing agent is removed by careful blotting, 

 with firm pressure, with two or more thicknesses of filter- 

 paper. A drop of thick solution of Canada balsam in 



* Oil of cloves will clear out of methylated spirit, but for xylol 

 or cedar oil absolute alcohol must be used. For many purposes 

 methylated spirit may be substituted for absolute alcohol, but 

 the ordinary commercial methylated is unsuitable, as it becomes 

 milky on the addition of water. The old methylated spirit 

 (alcohol and wood .spirit) must be used. 



