MODERN RESEARCHES INTO THE NATURE OF YEAST. 143 
ments ever takes place, even when all the conditions suitable 
for the development of fungi exist. With the third day the 
vegetation of the yeast gradually diminishes, and on the fourth 
the cells are all separate from one another and no new buds 
are produced. After growth has continued for about four 
days, many of the cells—the older ones, containing but little 
protoplasm—die away and collapse. Others swell up till 
they attain a diameter of ‘011 to ‘014 mm. The large vacu- 
oles have disappeared, the whole of the protoplasm appearing 
to be now interspersed with small vacuoles and drops of oil. 
On the fifth or sixth day, two, three, or four denser nuclei 
have become differentiated, almost all the remaining proto- 
plasm being collected round them in fine granules, the 
nuclei becoming surrounded in the course of twelve or four- 
teen hours by a delicate membrane.! The original cell then 
encloses, besides an extremely small quantity of protoplasm 
and watery cell-sap, two, three, or four roundish daughter- 
cells from ‘004 to ‘005 mm. in diameter, formed by free cell- 
formation (fig. 1, a, f). When these are four in number they 
res ae 
form across or tetrahedron, like pollen-cells or fern-spores in 
their mother-cell. ‘The membranes of the daughter-cells are 
always at first distinctly separated from the wall of the 
mother-cell; but subsequently the latter not unfrequently 
1 A very convenient method (devised by Professor Huxley) is to spread 
the yeast thinly on moistened cakes of plaster of paris and cover with a 
bell-jar. The yeast should be examined from day to day, and a little water 
poured under the cake when it becomes too dry. There is no trouble from 
bacteria or moulds, but the time required seems to be somewhat longer 
than with Reess’s method. A ‘culture’ of this kind started on March 2 
of the present year produced ascospores in abundance by March 13. 
WT. D. 
