PRESERVING AND STAINING 405 



on one side till the balsam sets. Throughout all these processes 

 the greatest care should be taken that the sections are never 

 without a covering of liquid. 



If permanent preparations are not required, such stains as 

 phloroglucin, aniline chloride, etc., can be employed to differ- 

 entiate the tissues, and the sections are usually mounted in 

 glycerine diluted with an equal volume of water. Preparations 

 can also be mounted in glycerine jelly, such mounts being much 

 more rapidly and easily prepared than those with Canada balsam, 

 but they often perish after a few years. 



The liquid stains most commonly employed are prepared as 

 follows : 



Aniline Blue. Saturated solution in alcohol or water, with 

 a trace of acetic acid. 



Bismarck Brown. Dissolve 2 grams in 100 c.c. of 70% alcohol. 

 Stain for about li minutes. 



Eosin. 1% solution in either water or alcohol. Stain for 

 3 to 5 minutes. 



Gentian Violet. I % solution in water. Stain for from 10 

 to 15 minutes, transfer to alcohol, and quickly counterstain with 

 Bismarck brown. 



Heematoxylin. Best bought prepared ready for use. 



Methyl Blue. Saturated aqueous solution. For live staining 

 this is greatly diluted. 



Safranin. 1% solution in 50% alcohol. 



VII. Measurement under the Microscope. This is accomplished 

 by means of an eyepiece micrometer and a stage micrometer 

 (both obtainable from the usual dealers in microscopic requisites) . 

 The stage micrometer is an ordinary slide on which is mounted 

 a millimetre scale, divided into tenths and hundredths, and 

 obtained by photographic reduction. The eyepiece micrometer 

 fits into the ocular, and consists of a scale that is usually 

 divided into a hundred equal parts. For each objective the 

 value of a division of the eyepiece micrometer is determined in 

 terms of the divisions of the stage micrometer (i.e. in hundredths 

 of a millimetre). If subsequently any object is measured with 

 the eyepiece scale, its actual size can be calculated. 



VIII. Section-cutting. During this operation both razor and 

 material should be kept moist with either water (for fresh 



