i 3 2 THE POPULAR SCIENCE MONTHLY. 



to receive the spirit distilled. The flame of small -wood-splinters being 

 applied to the boiler, after a time vapor rose into the head, passed 

 through the tube, was condensed by the cold of the water, and fell in 

 a liquid fillet into the bottle. On being tasted, it proved to be that 

 fiery and intoxicating spirit known in commerce as Kirsch or Kirsch- 

 wasser. 



The cherries, it should be remembered, were here left to themselves, 

 no ferment of any kind being added to them. In this respect what 

 has been said of the cherry applies also to the grape. At the vintage 

 the fruit of the vine is placed in proper vessels, and abandoned to its 

 own action. It ferments, producing cai'bonic acid ; its sweetness dis- 

 appears, and at the end of a certain time the unintoxicating grape- 

 juice is converted into intoxicating wine. Here, as in the case of the 

 cherries, the fermentation is spontaneous in what sense spontaneous 

 will appear more clearly by-and-by. 



It is needless for me to tell a Glasgow audience that the beer- 

 brewer does not set to work in this way. In the first place the brewer 

 deals not with the juice of fruits, but with the juice of barley. The 

 barley having been steeped for a sufficient time in water, it is drained, 

 and subjected to a temperature sufficient to cause the moist grain to 

 germinate ; after which, it is completely dried upon a kiln. It then 

 receives the name of malt. The malt is crisp to the teeth, and de- 

 cidedly sweeter to the taste than the original barley. It is ground, 

 mashed up in warm water, then boiled with hops until all the soluble 

 j)ortions have been extracted; the infusion thus produced being called 

 the wort. This is drawn off, and cooled as rapidly as possible ; then, 

 instead of abandoning the infusion, as the wine-maker does, to its own 

 action, the brewer mixes yeast with his wort, and places it in vessels 

 each with only one aperture open to the air. Soon after the addition 

 of the yeast, a brownish froth, which is really new yeast, issues from 

 the aperture, and falls like a cataract into troughs prepared to receive 

 it. This frothing and foaming of the wort is a proof that the fermen- 

 tation is active. 



"Whence comes the yeast which issues so copiously from the fer- 

 menting-tub ? What is this yeast, and how did the brewer become 

 in the first instance possessed of it ? Examine its quantity before and 

 after fermentation. The brewer introduces, say, 10 cwts. of yeast ; he 

 collects 40, or it may be 50 cwts. The yeast has, therefore, augmented 

 from four to five fold during the fermentation. Shall we conclude that 

 this additional yeast has been spontaneously generated by the wort ? 

 Are we not rather reminded of that seed which fell into good ground, 

 and brought forth fruit, some thirty-fold, some sixty-fold, some a 

 hundred-fold ? On examination this notion of organic growth turns 

 out to be more than a mere surmise. In the year 1680, when the 

 microscope was still in its infancy, Leeuwenhoek turned the instru- 

 ment upon this substance, and found it composed of minute globules 



