YEASTS 67 



of the S. cerevisia. After twelve hours of fermentation, the meta- 

 chromatic corpuscles become more numerous. At the same time, the 

 cytoplasm forms little vacuoles which contain no metachromatic cor- 

 puscles, but only glycogen, easily detected by iodo-iodide of potassium. 

 These are gradually fused into a single vacuole, which enlarges much 

 and modifies materially the cell structure. The glycogenic vacuole, 

 increasing, pushes back to the periphery of the cell the cytoplasm, the 

 vacuoles with metachromatic corpuscles, and the nucleus whose chro- 

 maticity increases and which becomes homogeneous in appearance 

 (Fig. 46, n). After forty-eight hours, moreover, the cell is found to 

 consist of an enormous vacuole filled with glycogen which occupies 

 most of it, while the nucleus, the vacuoles with metachromatic cor- 

 puscles and the cytoplasm are pushed back to one side of the cell, which 

 is then transformed into a kind of glycogen sack (Fig. 46, 12 and 13; 

 48, 6-8). At this time the glycogenic vacuole contains a great many 

 small granulations (Fig. 46, 12-13), which easily fix some staining 

 materials, especially ferric haematoxylin, and whose origin and signifi- 

 cance have not been determined. 



Toward the end of fermentation, the glycogen gradually diminishes 

 and the glycogenic vacuole is gradually reduced, then ends by dis- 

 appearing. The cell after this resumes its original structure. 



In the course of these phenomena, the membrane apparently shows 

 no modification. It is known, however, that under some conditions, 

 yeasts secrete gelatinous substances which englobe their cells in a kind of 

 jelly and so appear like zoogloea (Hansen). It is well to add, on the 

 other hand, that many pathogenic yeasts, when living in the host, have 

 the ability to protect their cells against the reaction of the organisms, 

 by secreting a very thick capsule of gelatinous nature: each of their 

 cells is then surrounded by a large capsule. 



CYTOLOGICAL PHENOMENA or THE SPORULATION AND GERMINATION 

 OF ASCOSPORES. For a study of the sporulation, we will consider a 

 representative of the species Schizosaccharomyces, the Sch. octosporus, 

 in which these phenomena are easily observed and especially well 

 understood. 



We know that in this yeast, as in some others, sporulation is pre- 

 ceded by a sexual phenomenon consisting of an isogamous copulation. 

 The ascus results from the fusion of two similar cells. The gametes are 

 ordinary cells which have the structure which we have previously 



