158 Modern Microscopy 



in Canada balsam, proceed to stain as above ; then make a 

 saturated solution of picric acid in methylated spirit, filter, 

 and dehydrate the section in it ; then give it a final rinse 

 in methylated spirit, clear in clove-oil and mount in Canada 

 balsam. 



Farrant's Medium. — Take of glycerine and a saturated 

 aqueous solution of arsenious acid equal parts, and mix 

 them well together ; then add as much powdered gum arabic 

 as the mixture will take up, and let it stand for six weeks. 

 Filter, and keep in an outside stoppered bottle. 



The above is difficult to make ; it is better to obtain it 

 ready for use. 



Glycerine Jelly. — Dissolve 1 ounce of French gelatine in 

 6 ounces of distilled water ; then melt in a water-bath, and 

 add 4 ounces of glycerine and a few drops of creasote or 

 carbolic acid. Filter through paper while warm, and keep 

 in a stoppered bottle. The above may be used instead of 

 Farrant's medium. The jelly must, of course, be warmed 

 before use. All tissues or sections must be well soaked in 

 water before they are mounted in Farrant's medium or 

 glycerine jelly, so that all trace of alcohol is removed. 



Tissues containing much air should be soaked in water 

 that has been boiled for about ten minutes and allowed to 

 cool. 



LESSON V. 



STAINING AND MOUNTING MICRO- 

 ORGANISMS. 



The investigation of bacteria may be carried out under 

 various conditions. 



(1) In fluids, such as milk, water, blood, pus, etc. 

 (2) On solid media, bread, meat, potatoes, meat jelly, 

 etc., or in the tissues and organs of animals. In the former 

 case a drop of fluid is placed on the centre of a cover- 



