216 Experiments on the Growth of Yeast. [Sess. 
settled. Several processes by which the rate of growth of 
the yeast, or, in other words, the conversion of the glucose into 
alcohol and carbon dioxide, could be ascertained were available, 
—as the periodical direct determination of alcohol or carbon 
dioxide formed, or the diminution of the amount of glucose in 
the various solutions, due to its gradual conversion into these 
substances ; or, again, by measuring the pressure of the evolved 
carbon dioxide, as adopted by Schultz and others. After full 
consideration, we concluded that there were objections to all 
these methods, and that for our purpose the simplest and 
most accurate process would be to ascertain, by weighing, the 
actual amount of carbon dioxide evolved from day to day. 
With this object twelve flasks, each having a capacity 
of about 200 ec, were taken and so fitted that the carbon 
dioxide produced by the fermentation was allowed to escape 
freely after passing through strong sulphuric acid to retain 
moisture, the entrance and final exit tubes of the apparatus 
being protected by tubes containing potassium hydrate and 
calcium chloride, to prevent absorption of moisture, &c., from 
the atmosphere. The flasks were numbered 1 and 2 and A, 
B, C, D, E, F, G, H, I, and K. Into each flask 80 cc. of the 
solution of glucose were introduced. Nos. 1 and 2 each 
received in addition 20 cc. of water, and to each of the — 
others was added 20 c.c. of arsenical solution, so as to give 
proportions of arsenious oxide ranging from 1 in 500 to 1 in 
60,000, as already indicated. To No. 2 and A, B, C, D, E, F, 
G, H, I, and K was added 20 cc. of brewer’s yeast, No. 1 
being left without. The flasks were then very carefully 
weighed, the potassium and calcium tubes being, of course, 
previously removed. The weighing was repeated daily at 
(with one exception) the same hour until the conclusion of the 
experiment, the loss of weight representing the amount of 
carbon dioxide evolved, and indirectly, of course, the amount of 
glucose converted by the process of fermentation into alcohol 
and carbon dioxide and the rate of growth of the yeast, from 
which the effect of the arsenious oxide in retarding or 
accelerating growth can be at once seen. 
We do not publish our weighings and calculations in detail: 
we have represented them in curves, which show our results 
at a glance. Plate XXV. is to compare the CO, given off by 
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