YEAST. 287 



Note that the growth of the Yeast (as judged by the 

 cloudiness and frothiness of the liquid) is arrested by a 

 very low temperature and is increased by warmth; the 

 liquid in F does not become frothy or smell of alcohol, the 

 Yeast having been killed by boiling; in A there is very 

 little growth, any that does occur being due to the fact that 

 the Yeast placed in the water contains enough food to last 

 for a short time. 



412. Budding of Yeast. Examine a drop of culture 

 solution containing actively growing Yeast, and note that 

 many of the cells are joined together in chains, often 

 branched, which have evidently been formed by a process 

 of budding, since the cells at the free end of each chain 

 are the smallest. 



In order to watch the actual budding process, place a 

 very little dry Yeast in a hanging drop of Pasteur's fluid 

 in a moist chamber slide ( 18), and examine it from time 

 to time ; note that the larger cells are evidently putting out 

 little projections, which may grow until they reach the size 

 of the parent cell, and that instead of being at once de- 

 tached the buds may in turn produce other buds, and these 

 yet others, until a chain is formed. 



Since the original cell may produce buds at two or more 

 points of its surface, radiating colonies may be formed, but 

 the outer cells of the chains become abstricted, each grow- 

 ing larger when free and budding in the same way as 

 its parent, and so on. 



413. Spore Formation. Under certain conditions the 

 cells of Yeast may produce resting-spores, the protoplasm 

 of the cell dividing into (usually) four portions which be- 

 come rounded off and acquire a thick wall, so that they 

 resist drought, and are on account of their minute size 

 readily wafted about in the air. The production of 

 abundant spores may be readily induced by one of the fol- 

 lowing methods : 



(1) Set aside a culture of Yeast in Pasteur's fluid with 

 sugar ; after a few weeks spores will appear. (2) Spread 



