Organic ferments. 215 



united; as many as a dozen remaining connected in one brmeh. The 

 principal difference between the two kinds is in the time taken for bud- 

 ding. 



The surface or high fermentation is the cheapest and quickest, but in 

 sedimentary, or low fermentation, the temperature is so much lower 

 that the adventitious germs that set up the vicious fermentations that 

 constitute the diseases of beer are rendered inactive, and as long as the 

 beer is kept cool it will retain its quality. Hops in beer are also used to 

 defend it against the parasitism of Bacteria, which are killed by them. 



As long as yeast is in contact with a fermentable liquid it grows only by budding, the 

 new buds carrying the line of vitality, while the old ones are being gradually disinte- 

 grated. But if this budding process is arrested without destroying vitality, under certain 

 conditions the organism goes to seed that is, forms spores, so called. This operation 

 can be brought about artificially by suddenly depriving the plant of nourishment, es- 

 pecially saccharine, and exposing it in a damp atmosphere or on a moist substance. 

 Rees obtained spores in 15 or 16 days by washing the yeast in clean water several times 

 during successive days, then decanting the water and drawing off all that was liberated 

 from the mass, day after day. 



Engel fixed up a contrivance, consisting of a mass of plaster of Paris, which he placed 

 in a dishjof corresponding shape- The t">p of the plaster he covered with yeast, fresh 

 and free as possible from all fermentable fluid. In the dish around the plaster he poured 

 water till it came within a centimetre (.39 in.) of covering the plaster. Over all he 

 placed a glass cover to keep off the spores of the air. (The plaster was to suck up and 

 supply steady moisture.) The vital energy of the yeast, now unable to construct any 

 more buds, expends itself in forming spores. The oldest cells and those most impover- 

 ished in protoplasm " perish and breakup." The more vigorous increase in size, their 

 lacunae (vacuoles) " disappear and the protoplasm is diffused uniformly in the cellular 

 juice." 1 In from G to ]0 hours from two to four "small islets" appear surrounded by 

 fine granulations. These islets are bright and dense and gradually assume a spherical 

 form. Twelve to 24 hours later each of these spherules is " invested with a membrane, very 

 thin at lirst but which thickens by degrees and then shows a double outline when mag- 

 nified 600 diameters." "The spore is then ripe. The mother cell thus contains from 

 two to four spores." During their evolution the spores touch each other, forming plane 

 surfaces at the point of contact. If there are only two spores each has a flat side; if 

 there are three, each has two flat sides at an angle of 120 to each other ; if there are four 

 each has three llat sides if they are piled up ; or only two at right angles to each other, 

 if the four cells lie in the same plane. "When the spores ripen the thecae( cases or 

 sheath^ > are moulded on them and thus assume their various forms. The theca of the 

 dyads is elliptical, that of the triads is triangular with rounded angles, that of the tetrads 

 in the shape <>!' a cros;," (i. e., in one plane ) "is in the form of adiamond with rounded 

 angles: in the tetnuls, piled upon eacli other, the theca is tetrahedral. " When in com- 

 plete maturity the, membrane of the sporecase, or mother cell, which has become a 

 fruit, is torn and allows the spores to escape. The theca3 themselves vary from .01 to 

 .015 of a millimetre ( .OO039 to .00047 of an inch ), and the spores from .004 to .005 

 of a millimetre ( .00015 to .00019 of an inch") This going to seed, or production of 

 spores, cannot take place in the absence of atmospheric or free oxygen. All the other 

 functions of yeast, including its growth by budding, are carried on at the expense of the 

 oxygen contained in the sugar of the infusion in which it works. 



The foregoing is :in account of Saccharomyces Cerevisiae, but some 

 oilier ferments will affect the alcoholic fermentation of glucose. Sao 

 c/Kirinui/crx Minnr is the name given to the ferment obtained from leaven 



of Hour (Kn.u-el). 



Tin 1 fermeiilafmn of a saccharine medium by this is slower than by 

 beer yeast. Spores enclosed in theeje are produced in this variety. 



1 The quotations are from Schut /en herder, on Fermentation. 



