78 Fermentation and Kindred Phenomena. 



It is by this process of budding that yeast usually multi- 

 plies ; but there is another method of reproduction which occurs 

 only under special conditions. In this method we find definite 

 seeds or spores produced in the cell. Spore formation occurs 

 when yeast is deprived of nourishment and is exposed to a damp 

 atmosphere. " Under these conditions the vegetative life of the 

 yeast ceases suddenly, and in a few hours we see great changes 

 take place in the protoplasm of the cells. The oldest and those 

 which are poorest in protoplasm die and break up. While 

 others grow larger, their lacunce disappear and the protoplasm 

 is diffused uniformly in the cellular juice. At the expiration 

 of from 6 to 10 hours we notice the appearance in the midst of 

 the protoplasm of from 2 to 4 small islets more brilliant and 

 dense than the rest, around which fine granulations collect. 

 These dense spots do not present any appearance of a nucleus, 

 and they become differentiated more and more until they are 

 exactly spherical ; 12 to 24 hours later each becomes invested 

 with a membrane, very thin at first, but which thickens by 

 degrees. The spore is then ripe." These spores or " ascospores" 

 as they are termed, are about \ the size of the mature yeast cell, 

 and they have a much higher degree of vitality than the cell 

 itself, and an infinitely greater power of resistance to destructive 

 agencies. Thus they may be completely dried, and even 

 exposed to a pretty high temperature, without losing their 

 power of germination. They are, in fact, similar to the seeds 

 of ordinary plants, and like many of these are distributed by 

 the air. I think we may compare yeast with a bulbous plant, 

 say a hyacinth, which at times reproduces itself by subdivision 

 of the bulb, at others by the production of true seeds. Now, 

 the ascospores of yeast are found in ordinary dust ; and as grapes 

 and other fruits are exposed for a long time during their growth 

 to the atmosphere, a layer of dust collects on their surface and 

 mixes with the juice when the fruit is crushed. Hence we can 

 easily understand the spontaneous fermentation of grape juice 

 and the juices of other fruits, such as those of apples and pears. 

 Indeed, the spores of yeast have been found on the skin of the 

 grape. 



Let us return for a few moments to the process of fer- 



