The most striking phenomena of fermentation are the turbidity of the liquid, the rising of gas bubbles to the surface, and the increase in temperature, the disappearance of the sugar, the appearance of alcohol and the clearing of the liquid. At the end a slight scum is formed on the top of the liquid and a light colored deposit at the bottom. This deposit consists of yeast which is capable of exciting the vinous fermentation in other solutions of sugar. The lower the temperature the slower the process, while at a temperature above 86∞ F. the vinous fermentation is liable to pass into other forms of fermentation to be hereafter considered. There are many theories of fermentation, of which the two most important are those of Pasteur and Buchner. The first teaches that fermentation is caused purely by the organic life of the yeast plant and is not a mere chemical action, whereas the second view most largely held to-day is that fermentation is a purely chemical change due to certain unorganized substances called "enzymes" present in the yeast. The theory need not detain us. It is sufficient that the yeast plant in some manner acts to decompose the saccharified mash into alcohol and carbonic acid gas. =Yeast= is a fungus, a mono-cellular organism, which under proper conditions propogates itself to an enormous extent. There are many races or varieties of yeast each having its peculiar method of growth. For our purposes we may divide the yeast races into two classes, wild yeast and cultivated yeast. Originally any of the yeast races were supposed to be good enough to effect fermentation but to-day every effort is made to procure and use only those races which have the greatest power to decompose sugar. It was for this reason that the old distiller kept portions of his yeast over from one fermentation to the next. This was yeast whose action they understood and whose abilities were proven. This yeast so kept was open, however, to the chance of contamination and yeast to-day is as carefully selected and bred as is a strain of horses, or dogs, or plants. After getting a portion of selected pure yeast for breeding purposes, it may be sowed, that is, propagated very carefully in a yeast mash, in sterilizing apparatus, where all chance of contamination by bacteria or wild yeast is avoided. From this bed of mother yeast, or start yeast, the yeast for the successive yeast mashes is taken. The preparation of the various varieties of yeast mashes is too lengthy to be set forth except in special treatises on the subject, but the ordinary method of yeasting is as follows, reference being made to Fig. 5, which shows the apparatus used in the yeasting and fermenting departments of a distillery, as installed by the Vulcan Copper Works, of Cincinnati. The yeast tubs are shown to the left of the illustration. They are each provided with cooling coils and stirrers.