908 
THE PHARMACEUTICAL JOURNAL AND TRANSACTIONS. 
[May 13, 1871, 
large blocks of chalk taken at a depth of 200 feet from 
the surface of the soil out of a tunnel driven in a 
mountain, large quantities of microscopic animalcules, 
which he has named Microzyma Cctcc ; and he also states 
that if some of this chalk he placed in a saccharine 
solution, lactic and butyric acid fermentation ensue. 
Yeast is so well known that its description here is 
quite unnecessary, and the fact that it converts sugar 
into alcohol is patent to all. The chemical formula of 
this change is thus:—- 
Ci 2 H 12 0 12 = 2C 4 H f) Oo + 4C0 2 
Grape Sugar. Alcohol. Carbonic Acid. 
A east is supposed to be the conidial condition of 
Temcilhum glaucuin , but much light is required to be 
thrown on this matter to raise it from its present ob¬ 
scurity. 
The yeast cells consist of an outer membrane of ccllulin 
—the same material as the cellular tissue of other vege¬ 
tables—in the interior of which is a highly complex 
gelatinous substance allied to albumen. 
The appearance of yeast under the microscope varies 
considerably with its condition; when at rest, that is, 
when fermentation is arrested, its form varies from 
globular to ovoid, frequently with an uneven outline, 
as if the cells were very partially empty; but when 
they are put. into a fresh solution of sugar they swell 
out, and during active fermentation appear globular or 
nearly so, and more transparent than before. 
When yeast is added to brewer’s w-ort it increases 
rapidly, and grow's to six or eight times its original 
quantity during fermentation; the wort being a solution 
which contains in abundance the elements required for 
its development, namely, grape sugar and some albu¬ 
minous substances derived from the malt and hops. 
During fermentation these albuminous matters dis¬ 
appear from the solution in proportion to the develop¬ 
ment of the yeast, and the sugar also disappears in the 
same ratio. When the fermentation is complete, we 
find that in place of the complex albuminous matters in 
.the wort, we have, simpler chemical combinations, such 
as salts of ammonia, and in place of the sugar we have 
alcohol. Jhese ^chemical changes take place simul¬ 
taneously ; but with this important difference, that the 
amount of nitrogen in the original wort is reduced by 
about one-half, while the alcohol and carbonic acid 
nearly correspond to the weight of the sugar, the re¬ 
mainder being converted into lactic acid, etc., a small 
quantity of which is always formed during vinous fer¬ 
mentation. But the yeast consisting almost entirely of 
albuminous matters, and having increased to several 
times its original quantity, fully accounts for the dis¬ 
appearance ot so large a proportion of the nitrogen from 
the wort. 
Thus it will be easily understood that yeast, in order 
to grow, must be supplied with some soluble azotized 
matter, such as albumen; and it is as easily proved that 
it will not grow without. 
To ferment one hundred parts of sugar, one part of 
yeast is required; when the fermentation is complete, 
the yeast is exhausted, and in its place ammoniacal salts 
and cellulin are found. As the vinous fermentation takes 
pl a oc only during the growth of the yeast, it may be said 
tnat it wall grow in simple saccharine solutions. In a 
certain sense this is correct, but such growth is degene¬ 
rate and exhaustive, and not the healthy growth which 
increases and multiplies, for in such a solution the yeast 
posrti\ ely lives on its own substance: this has been proved 
by Pasteur in the following manner:—“He took a quan¬ 
tity ot washed yeast and divided it into two equal por¬ 
tions,—one of these was placed in a solution of pure 
sugar, the other portion was boiled in water, the de¬ 
coction filtered, and the filtrate added to a similar solu¬ 
tion of sugar, to which a very minute quantity of fresh 
yeast was added. In the first case twelve parts of sugar 
were converted into alcohol in six days, when the yeast 
became exhausted. In the second case the liquid became- 
turbid; fresh yeast was formed at the expense of the 
azotized matter derived from the boiled yeast, and ten 
parts of sugar were fermented in nine days.” 
Some years ago, when experimenting on bread-making 
I was much puzzled by finding that when the yeast was 
thoroughly washed the sponge did not rise so quickly, 
nor was the bread so light as when made with yeast as 
received from the brewery. I have since learned that a 
portion of the yeast is soluble in water, and that when it 
has been dissolved out by washing, the yeast is less 
active; on exposure to the atmosphere, however, it re¬ 
covers its activity. 
Yeast causes a curious and important change to take- 
place when added to a solution of cane sugar, converting 
it into fruit sugar by causing it to combine with one 
equivalent.of water, during which operation the solution 
increases in specific gravity. This transformation is 
attributed to the soluble portion of the yeast; but be 
this as it may, some of it is evidently destroyed by the 
process, as a larger proportion of yeast is required ta 
convert cane sugar into alcohol than grape sugar. It is- 
a fact scarcely known to brewers, who use it, that cane i 
sugar cannot be fermented into alcohol; for although* 
when yeast is added to a cane sugar solution the vinous, 
fermentation eventually ensues, it nevertheless does not 
commence until the yeast, without any apparent change- 
in itself,, has transformed the whole of the cane sugar- 
into fruit sugar. The progress of this transformation 
may be witnessed by polarized light: the cane sugar 
producing a right-hand rotation of the ray= 73°, while 
the fruit sugar causes a left-hand rotation of 26°. 
I have one more observation to make in reference to 
yeast. . When it has been kept some days, of course, 
according to temperature, it loses the pleasant smell it 
had when fresh, and acquires some fermentive properties,, 
which, as far. as I am aware, have not received much at¬ 
tention. It is well known to brewers that if the yeast 
be allowed to stand on the beer for a day or two after 
fermentation has been stopped, a very disagreeable effect, 
is produced; the beer is not acetified, but the flavour is 
entirely changed; it is unpalatable, and the brewers call 
it yeast-bitten. 
Now I am not in a position to throw any light on 
this change; but if stale yeast be examined with the 
microscope, there will be found interspersed among the 
ordinary cells a large number of minute globular bodies, 
which are generally in motion; and I have also noticed 
a larger proportion of short, straight vibrio-like bodies,, 
than are to be found in yeast during active fermentation. 
Whether these organisms produce the disagreeable 
effects referred to, I am unable to say, and merely point 
to them as one of the changes which take place in yeast 
when left to itself. 
Diastase is a ferment, which has the property of con¬ 
verting starch into sugar, by causing it to assimilate 
the elements of water without evolving any gaseous 
products. 
The transformation is represented thus :— 
<AH lt ,O 10 + 2HO = C 12 H 12 0, 2 . 
Starch. Vfater. Sugar. 
Diastase is extracted from malt by soaking it in¬ 
water, in which, at moderate temperature, it is soluble;_ 
it may be taken as the type of the ferments produced in 
all germinating seeds,—for as all seeds contain starch, 
which must be rendered soluble in the form of sugar- 
before it can become food for the embryo—so they all 
contain some azotized matters, as albumen, gluten, etc., 
which are capable of passing into the form of a ferment,., 
allied to diastase. 
(To be continued.') 
