164 Proceedings of Royal Society of Edinburgh. [sess. 
Abstract of Paper on the Rate of Fermentation of 
Sugars.” By W. G. Aitchison Robertson, M.D., D.Sc., 
F.R.C.P.E. (From the Physiological Laboratory^ University of 
Edinburgh.) 
(Read January 29, 1894.) 
Most of the sugars undergo certain fermentations, the chief of 
these being the lactic, butyric, and the alcoholic or vinous. 
To determine the rate at which fermentation occurs in the com- 
moner varieties of sugar, I performed the following experiments. 
I. Lactic Acid Fermentation. 
I made 5 per cent, solutions in distilled water of chemically pure 
samples of cane sugar, invert sugar,* lactose, dextrose, maltose, and 
Isevulose. 100 c.c. of each of these solutions were placed in 
separate flasks, and to each of them 10 c.c. of sour skim-milk filtrate 
were added, and the degree of acidity immediately estimated, 
calculating it as lactic acid. This I have termed the initial acidity. 
During the succeeding four days the flasks were kept at a uni- 
form temperature of 38° C., which is most suitable for the growth 
of the bacterium lactis. The percentage of acid produced in each 
solution was estimated at intervals, and the amount of lactic acid 
formed in definite periods is shown in Table I. 
Table I. — Total Percentage amounts of Acid formed in 
stated Periods. 
Hours. 
Cane 
Sugar. 
Invert 1 
Sugar. 1 
Lactose. 
Dextrose. 
Maltose. 
L^evulose. 
2 
0 
0-0018 
0-0009 
0.0018 
0-0009 
0-0018 
4 
0 
0-0031 
0-0018 
0-0036 
0-0012 
0-0027 
8 
0-0063 
0-0090 
0-0027 
0-0045 
0-0036 
0-0054 
24 
0-0072 
0-0135 
0-0045 
0-0054 
0-0045 
0-0072 
72 
0-0405 
0-0423 
0-0603 
0-0512 
0-0315 
0-2691 
The invert sugar was made by rendering the 5 per cent, solution of pure 
cane sugar slightly acid with sulphuric acid (this is the most powerful acid 
