232 ELEMENTS OF BOTANY 
EXPERIMENT XXI 
Can Yeast grow in Pure Water or in Pure Syrup ?— Put a bit of 
compressed yeast of about the size of a grain of wheat in about four 
fluid ounces of distilled water, and another bit of about the saine size 
in four fluid ounces of 10 per cent solution of rock candy in distilled 
water; place both preparations in a warm place, allow to remain for 
twenty-four hours, and examine for evidence of the growth of the 
yeast added to each. 
298. Size, Form, and Structure of the Yeast-Cell. — The student 
has discovered by his own observations with the microscope that the 
yeast-cell is a very minute object, — much smaller than most of the 
vegetable cells which he has hitherto examined. The average diam- 
eter of a yeast-cell is about 3755 of an inch, but they vary greatly 
both ways from the average size. 
The general form of most of the cells of ordinary yeast is some- 
what egg-shaped. The structure is extremely simple, consisting of 
a thin ce]l-wall, which is wholly destitute of markings, and a more 
or less granular semi-fluid protoplasm, sometimes containing a por- 
tion of clearer liquid, the vacuole, well shown in the larger cells of 
Fig. 1662 
299. Substances which compose the Yeast-Cell. — The cell-wall is 
composed mostly of cellulose; the protoplasm consists largely of 
water, together with considerable portions of a proteid substance,? 
some fat, and very minute portions of sulphur, phosphorus, potash, mag- 
nesia, and lime. It is destitute of chlorophyll, as would be inferred 
from its lack of green color, and contains no starch, 
1 This is not the ordinary commercial yeast. 
2Jt may be found troublesome to apply tests to the yeast-cell on the slide, 
under the cover-glass. Testing a yeast cake is not of much value, unless it 
may be assumed that compressed yeast contains little foreign matter and con- 
sists mostly of yeast-cells. Still the test is worth making. Millon’s reagent 
does not work well, but the red or maroon color which constitutes a good test 
for proteids is readily obtained by mixing a teaspoonful of granulated sugar 
with enough strong sulphuric acid to barely moisten the sugar throughout, 
and then, as quickly as possible, mixing a bit of yeast cake with the acid and 
sugar. A comparative experiment may be made at the same time with some 
other familiar proteid substance, e.g., wheat-germ meal. 
