306 Botanical Society of Edinburgh : — 



size of the maternal cell. There can, however, bu no stated time for 

 these changes, for they vary with the temperature. In distillery- 

 wash, which is worked at a much higher temperature than brewery- 

 wort, the process begins much sooner, and is sooner completed ; and, 

 as might be inferred from the fact of their rapid growth, the cell- 

 walls are much thinner in the former than in the latter. One very 

 important fact results from this, viz. that yeast which has been 

 worked at a high temperature loses a considerable amount of its 

 activity. It is, in fact, " forced ;" and if yeast of this kind be applied 

 at once to work at a lower temperature, the process of fermentation 

 will be late in commencing, and will often stop. If, however, the 

 yeast be allowed to stand for a day or two, it recovers some of its 

 activity, but it is never so good for working at a lower temperature ; 

 and, therefore, as a general rule, yeast should always be worked at a 

 higher temperature in each succeeding operation ; that is, it should, 

 if possible, be worked in cool wort before being applied to wort which 

 requires to be worked at a greater heat. As soon as the jVrocess of 

 fermentation has attained its maximum, the budding begins to de- 

 cline, and ceases towards the close of the operation. The cells, 

 which were before of very variable size, now become more uniform, 

 and the nebulous mass in their interior assumes a more definite out- 

 line, and appears to be finely granular. After remaining on the 

 liquor for five or six days, a portion of the cells which are exposed 

 to the atmosphere become oval, and then elongated into tubes, mul- 

 tiplying still by gemmation and fissiparous division. Similar forma- 

 tions are also found in the sediment of the tun. This is the first 

 stage in the formation of the mycelium, and exercises an influence 

 of an important kind over the fermentation of the liquor. The 

 subsequent changes consist in the formation of a mycelium com- 

 posed of a network of ramifying tubes. These tubes are identical 

 in form with those given in a previous paper, and need not therefore 

 be again described. The perfect fructification in the specimens 

 which I have examined is that of Aspergillus glaucus, but there 

 can be no doubt, as I have before remarked, that other species and 

 genera are also present. In proof of this, a series of experiments 

 were made in Messrs. Jeffrey's brewery, with the following results : 

 1st, A quantity of mixed PenicilUa and Aspergilli (P. glmicum, 

 Asp. glaucus, A. nigrcscens, &c.) were placed in a gallon of wort, 

 at a temperature of 65° Fahrenheit, and allowed to stand in the tun- 

 room. On the second day the surface was covered with specks of 

 foam. On the third day the fermentation had fairly set in, and the 

 surface became coated with pale yeast, which, under the microscope, 

 exhibited oval non-nucleated cells in a state of gemmation. On the 

 fourth day, the fluid gave off a nauseous ' foxy ' odour, which disap- 

 peared on the sixth day, when the yeast-cells were observed to have 

 become spherical, and in all respects like good yeast. On the eighth 

 day the yeast was removed from the surface, and applied to a fresh 

 quantity of wort at the same temperature. This entered into fer- 

 mentation on the first day, and exhibited all the characters of perfect 

 yeast. The second experiment was made by placing a portion of 



