272 YEASTS AND YEAST-LIKE FUNGI 



and the granule behave identically toward certain vital stains, indi- 

 cates that they are both of the same nature. The granules repre- 

 sent some of the material of the vacuole which has temporarily co- 

 agulated. In older cells additional smaller vacuoles are found, and 

 sometimes granules of the same material not within a vacuole. 



In slides fixed by the usual procedures, the material in the vacu- 

 oles coagulates and becomes shrunken and distorted, appearing as 

 irreguar masses in the cytoplasm. They take the basic dyes in- 

 tensely and in general stain as does the chromatin, but may be 

 differentiated from the nucleus by various methods. They are most 

 beautifully demonstrated, however, by vital staining with neutral 

 red. Some of the cells suspended in water are placed under a cover 

 glass and a drop of 1 per cent aqueous solution of neutral red is 

 applied to one edge of the cover slip. As this seeps under, a solution 

 of graded concentration is formed, and in some part of the field the 

 right concentration will be found. Dead cells stain a uniform red 

 with this dye, but in living cells only the volutin vacuoles and gran- 

 ules will stain, the former a light pink, the latter a deep red. 



It is generally agreed that the volutin of the yeasts and bacteria 

 is a reserve substance identical with the yeast nucleic acid of the bio- 

 chemists and is closely related chemically with the thymonucleic 

 acid found in the nucleus. It differs from thymonucleic acid in that 

 it yields (i-ribose rather than d-desoxyribose and uracil rather than 

 thymine among its hydrolytic products. The amount of volutin de- 

 veloped in the cells appears to be proportional to the amount of 

 nucleic acid which can be extracted, and also to a certain extent to 

 the phosj^horus available in the medium. The volutin may be absent 

 in very young cultures, accumulates in large amounts in old cultures, 

 particularly in the "Dauerzellen," and is used up or disappears in 

 spore formation. 



Classification of Yeasts. The yeasts have been variously classi- 

 fied. Formerly the system of Guilliermond "^ found in his excellent 

 monograph was widely used and is still very useful. Recently, how- 

 ever, two monographs, one on the spore-bearing yeasts by Stelling- 

 Dekker -" and one on the asporogenous yeasts by Lodder,^* have ap- 

 peared. It is to be hoped that the third volume * promised by the 

 "Centraalbureau voor Schimmelcultures" of Baarn, Netherlands, 



* This volume was published in 1942 but was not distributed until late in 

 1945 in the United States: H. A. Diddens, and J. Lodder, Die anaskosporogenen 

 Hefcn, 2te Halfte, 511 pp., N.V. Noord-Hollandsche Uitgevers Maatschappij , 

 Amsterdam, 1942. 



