VEGETATION IN THE SEDIMENT 167 



are necessary for the identification of yeasts. To simplify matters, 

 let us suppose that we have isolated a yeast which we wish to iden- 

 tify, to determine whether it is a new variety or whether it is a variety 

 already known. 



Character of the Vegetation in the Sediment 



The preliminary examination ought to be concerned with the 

 sediment. Finally the microscopic features of the cells should be 

 investigated. 



Characteristics of the Sediment: The microscopic investigation 

 of the sediment of yeast growth ought to give very useful data. It 

 may be able to remain distributed through the medium or fall to the 

 bottom. Possibly it will attach itself to the sides of the culture flask. 



Shape and Dimensions of the Cell: The second step in the ex- 

 amination should be the microscopic examination of the cells taken 

 from the sediment of a culture in carbohydrate media. Hansen 

 recommended for this study a young culture grown at 25 for 24 hours 

 or for 3 or 4 days at room temperature. The dimensions of the cells 

 are variable characteristics. Beauverie 1 has recently applied bio- 

 metric methods to the yeast. For this 100 cells are taken from a cul- 

 ture and the measurements plotted against the corresponding cell. In 

 this way a curve may be drawn and a polygon made which will ex- 

 press the frequency of certain sizes. From the appearance of this 

 polygon, one may characterize the species. 



The genus Saccharomycodes is easily distinguished by the elongated 

 tubular cells and their mode of multiplication, which is intermediate 

 between budding and fission. In the same way, it is not difficult to 

 distinguish a budding yeast from the Schizosaccharomyces. Certain 

 yeasts of the genera Torulaspora and Debaromyces and many varie- 

 ties of the Torula possess a sufficiently characteristic spherical shape 

 with a great globule of fat. Other yeasts are elongated or cylindrical 

 and bud at their extremities. (Fig. 4.) 



Aside from these yeasts which we have mentioned and which 

 possess some morphological characteristic to differentiate them, the 

 great majority of the yeasts are not so characterized. Most of them 

 may not be separated by some quick microscopic feature. Some of 

 them may be grouped together by their shape but no separation may 

 be made between them by it. The microscopic examination of a yeast 

 tells us nothing about its genus or family. 



Optimum Temperatures and Limits for Budding : With regard to 

 budding there are maximum, optimum and minimum temperatures 



1 Beauverie, J. Les methodes de la biometrique appliquee a 1'etude de levures. 

 Comp. Rend. Soc. Biol. 1912. 



