THE MEMBRANE 45 



the majority of yeasts, they appear especially during sporulation and 

 serve as food for the ascospores. They are, then, reserve products. 

 Fat globules are also observed in old cells, but in this case seem to be 

 due to a degeneration of the cytoplasm. 



The Membrane 



The membrane of the yeasts is thick and presents a double layer 

 quite distinct. With the exception of S. granulatus, it is provided 

 with isolated granulations which are placed in regular fashion. We 

 have seen also that the ascospores of certain yeasts may offer a 

 warty membrane. The chemical constitution of the membrane is 

 only slightly known. 



According to chemical analyses of Schlossberger, it contains a 

 special cellulose which resembles fungine or metacellulose, and is 

 distinguished from the true cellulose by its insolubility in ammoniacal 

 cupric oxide, and reacts differently toward iodin. 



Liebermann and Bitto in treating yeasts successively with acids 

 and alkali obtained a cellulose which gave the zinc chloride reaction. 



According to Salkowski, this cellulose is colored brown by iodin. 

 Meigen and Spreng 1 claimed that they did not secure the true 

 cellulose from yeast membrane but a hemicellulose which was easily 

 hydrolyzed by the prolonged action of acids and alkalis. On the 

 contrary, according to Will and Casagrandi, the membrane was not 

 colored by iodin nor by the ordinary stains for cellulose. They 

 found no cellulose. According to Casagrandi, 2 pectose makes up 

 the membrane. Mangin 3 believed that it was composed of callose. 

 Tan ret and Visselingh found chitin in the membrane of beer yeast. 

 Whatever is the case, the membrane stains blue with Ehrlich's methyl- 

 ene blue and Hanstein's aniline. This membrane is especially visible 

 in the durable cells in which it thickens considerably. 



According to Will and Casagrandi, the membrane of the durable 

 cells is made up of two layers. (Fig. 10.) When the yeast is treated 

 with 4 or 5 per cent hydrochloric acid, washed and dried, and stained 

 with fuchsin according to the method of Strasburger, the outer layer 

 takes a violet red color which is surrounded by a colorless layer. 



Yeasts secrete under certain conditions mucilaginous substances 

 which collect the cells into a sort of network quite similar to zo- 

 ogloea. Hansen first attracted attention to this phenomenon which 



1 Meigen and Spreng. Ueber die Kohlhydrate der Hefe. Zeitschr. Phys. 

 Chemie, 55, 1908. 



2 Casagrandi, O. Saccharomyces ruber. Ann. d'Igi sperim. 7 and 8, 1898. 



3 Mangin, L. Observations sur la constitution de la membrane chez les 

 Champignons. Comp. Rend. Acad. des Sciences, 107, 1893. 



