94 A MANUAL OF BACTERIOLOGY 



and filtered through muslin, and to every 100 c.c. of the 

 mixture 1 grm. of sodium salicylate is added. The slide 

 is smeared thinly with this, the section is transferred to it 

 and afterwards dried in the manner above described. 



Supposing that the sections, in spite of all precautions, 

 curl up as they are cut, it is still often possible to obtain 

 a few that can be mounted. They may sometimes be 

 unrolled by cautious manipulation with a couple of 

 needles after having been softened by warming, or a 

 needle or knife- blade may be held close to the edge of 

 the microtome knife during cutting, so that curling is 

 prevented. 



Tissues embedded in paraffin may be kept indefinitely in labelled 

 pill-boxes and cut all at once or from time to time as required, or 

 the ribbons of sections may be preserved in a box in a cool place 

 until wanted. The slides also, with the sections attached, can be 

 kept until it is convenient to stain, if preserved free from dust in 

 a slide box. 



Cover-glass and Film Specimens 



The satisfactory preparation of cover- glass and film 

 specimens is one of the most important in bacteriology, 

 for they are used for the examination of cultivations of 

 bacteria, and of blood or other fluids or secretions, organs, 

 etc., for the presence of micro-organisms. 



Films and smears are now usually made on the slide, 

 but may be made on the cover- glass (" cover- glass speci- 

 mens "). In either case the glass must be clean and free 

 from grease. Cover- glasses must be thin, otherwise the 

 higher powers cannot be employed to examine the prepara- 

 tions, and those described as " No. 1 " should be purchased, 

 " f-in. squares " being a convenient size. These serve 

 both for cover- glass specimens and for covering sections ; 

 it is well also to have a few of the same thickness but 

 larger, viz. |-in. or 1-in. squares, for large sections. 



