METHODS OF STUDYING THE YEASTS 161 



Perenyi's Fluid: 



Chromic acid, 5 per cent 3 parts 



^Nitric acid, 10 per cent 4 



'Alcohol, 95 per cent 3 " 



The period of fixation ought to be about 12 hours. Finally, stain- 

 ing is accomplished with Heidenhain's ferric hemotoxylin (mordant- 

 ing with a 2| per cent solution of ammoniacal ferric alum, washing 

 rapidly in water and staining in a 1 per cent aqueous hematoxylin 

 solution). By this procedure a satisfactory differentiation of the 

 nucleus is obtained. The basophile grains stain quickly but the meta- 

 chromatic corpuscles generally do not. The hematoxylin method 

 of Delafield gives good result after fixation in Bourn's solution. These 

 methods at once allow the differentiation of the nucleus, which appears 

 with a diffuse tint, and the metachromatic granules, which take on a 

 wine color. The preparations thus prepared ought to be preserved 

 in Kayser's gelatin-glycerol mixture in preference to Canada balsam 

 which always causes a contraction of the cells. 



Alcohol, formalin and Lenhossek's fluid * are the most useful fix- 

 ing solutions for the metachromatic granules; they are not to be 

 recommended so highly for the nucleus. Unna's polychrome blue, 

 CresyFs blue and methylene blue, employed in 1 per cent aqueous 

 solutions, allow differential staining of the metachromatic corpuscles 

 but generally differentiate the nucleus quite badly. The preparations 

 obtained by these dyes decolorize rather quickly in the gelatin-glycerol 

 solution and are able to be preserved only in Canada balsam. 



To demonstrate glycogen, Lugol's solution (iodin in potassium 

 iodide) may be used. For fats, Flemming's solution 2 should be used. 

 The preparations are fixed in it and the fat globules are browned 

 by it, 



Methods for Determining the Properties of Yeasts towards Sugars: 

 It is often very desirable, especially when investigating a new yeast, 

 to determine its action towards sugars. The action of yeasts towards 

 such hydrocarbons constitutes a very important step in their dif- 

 ferentiation. The simplest method is that devised by Lindner. 3 It 



1 Lenhossek's Fixing Fluid: 



Mercuric chloride (sat. in water) 75 volumes 



Absolute alcohol 20 " 



Acetic acid 3 " 



2 Flemming's Solution: 



Osmic acid, 1 per cent in water 15 parts 



Crystallized acetic acid 1 " 



Chromic acid, 2 per cent in water 4 " 



3 Lindner, P. Mikroskopische Betriebskontrolle in den Garungswerben. 

 Paul Parey, 6th Edition, Berlin. 1909. 



