468 A MANUAL OF BACTERIOLOGY 



Another point in the identification of species of yeasts is the 

 period of formation of films. If the yeast is grown in wort with 

 free access of air and is undisturbed, e.g. in a beaker capped with 

 filter-paper, after a varying period a film composed of a zooglosal 

 mass of cells appears on the surface. 



If yeast, or disintegrated yeast-cells, be injected into animals, 

 the blood acquires specific agglutinative properties, agglutinating 

 the yeast-cells of the species with which the inoculation has been 

 carried out. 1 



On the yeasts of fermentation, see Jorgensen, Micro-organisms 

 and Fermentation, 4th ed., 1911 (C. Griffin and Co.), (full bibliog.) 

 Klocker, Fermentation Organisms. 



Examination of Yeasts 



The yeasts can be readily examined in the fresh state in hanging- 

 drop preparations. The cells should be young or they will not be 

 of the typical form ; a two or three days' old culture in wort or 

 grape-sugar solution may be used. The yeasts grow well at 20- 

 30 C. on the ordinary gelatin, agar, and potato, but wort gelatin 

 or wort agar is to be preferred. The elongated cells, common to all 

 old cultures of yeasts, may be obtained from the films which form 

 on wort cultures in wide flasks or beakers after two or three weeks. 



In order to stain yeasts, a dilution of the culture should be made 

 in a watch-glass of water, so that the cells may be isolated, as they 

 become distorted if groups form in the preparations. 



If the yeast has been grown in wort, it is best, before staining, 

 to pour off the fluid from the deposit of cells at the bottom of the 

 flask or test-tube, add some physiological salt solution and shake, 

 then allow the vessel to stand for an hour for the cells to sediment, 

 or centrifuge, and the process of washing may be repeated once. 

 Films may be prepared in the ordinary way and stained for five 

 minutes in Loffler's methylene blue, washed in water, dried, and 

 mounted. Or the films, after air-drying, may be fixed by immersion 

 in equal parts of alcohol and ether for ten minutes, dried in the air, 

 and stained as before. The preparations can also be stained in 

 gentian violet or fuchsin, or by Gram's method. 



Ascospores may be double stained by preparing films of a sporing 

 culture in the ordinary way, staining with carbol-fuchsin for two 

 minutes, rinsing in water, decolorising with 5 per cent, sulphuric 

 acid and with alcohol, rinsing in water, counter -staining with 

 Loffler's blue for five minutes, washing, drying, and mounting. 

 The spores are red, the remainder of the cells blue. 



1 See Macfadyen, Centr. f Bakt. (l te Abt.) ; xxx, 1901, p. 368. 



