EXAMINATION OF YEASTS 317 



a compound spore divided into several chambers. During 

 germination the spores swell, and the wall of the mother- 

 cell, which was originally thick and elastic, becomes 

 stretched thinner, and finally becomes ruptured, and then 

 remains as a loose shrivelled skin partially covering the 

 spores, or it becomes gradually dissolved during germina- 

 tion. The importance of this method of examination is 

 seen from the following fact : The Sacch. cerevisice does not 

 form spores until a period of ten days has elapsed ; whilst, 

 on the other hand, the Sacch. pastonanus II. (the most 

 common ' wild ' yeast), when kept under exactly the same 

 conditions, gives evidence of the commencement of spore- 

 formation after seventy-seven hours. 



(c) The Forination of Films. — Hansen subjected the films 

 which appear on the surface of fermenting liquids to a 

 thorough examination. To produce these films, Hansen 

 proceeded as follows : Having obtained his pure cultivation, 

 drop cultures were made into four-ounce flasks, half filled 

 with sterilised wort, and protected from falling particles 

 by being covered by a well-fitting cap. The films first 

 appear as small opaque points, which gradually increase in 

 size and then run together, forming irregular patches 

 floating on the upper surface of the liquid. As soon as 

 the film becomes apparent to the naked eye it is examined. 

 The film at' length overspreads the whole surface of the 

 liquid, and becomes adherent to the walls of the flask. A 

 very necessary condition for the formation of films is perfect 

 rest of the liquid in which they are being formed. 



The following tables, compiled by G. H. Morris {J. S. C. I., 

 1887, p. 119), show the differences exhibited by a number 

 of varieties of yeasts examined by Hansen's methods, with 

 respect to the formation of ascospores and films respec- 

 tively : 



