s 
BULLETIN 202, U. S. DEPARTMENT OF AGRICULTURE. 
alcohol test and the acidity of milk. Ramnistedt (25) also agrees 
with Fendler and Borkel, so far as he found, that no consistent 
relation existed between the alcohol test and the acidity of milk. 
He considers that the test gives preliminary knowledge of the hygienic 
quality of a milk. 
It is evident from the literature that in a mixed market milk the 
acidity plays a part in connection with the alcohol test, so that in 
considering the factors which influence the test we may first take up 
the question of acidity. 
THE INFLUENCE OF ACIDITY ON THE ALCOHOL TEST. 
In our first experiments the acidity of milk was raised by the 
addition of N/10 lactic acid. The results of two experiments recorded 
in Table 3 show that a very slight increase in the acidity of milk may 
cause a positive alcohol test with 75 per cent and 68 per cent alcohol, 
but a considerably higher acidity is required to cause a positive test 
with 44 per cent alcohol. 
These results show clearly that the alcohol test is sensitive to slight 
changes in acidity when these changes are produced by the addition 
of lactic acid. Since an increase in acidity will cause a positive 
alcohol test it is evident that the growth of acid-forming bacteria in 
milk will cause a positive test. 
Table 3. — Influence of acidity on the alcohol test. 
N/10 lactic 
Alcohol test 
acid added 
to 50 c. c. 
Acidity. 
of milk. 
75 per cent. 
68 per cent. 
44 per cent. 
c. c. 

1.81 
0.5 
1.88 
— 
_ 
_ 
1.0 
1.94 
i+M 
+M 
_ 
3.0 
2.21 
+ L 
+ L 
_ 
3.5 
2.38 
+ L 
+ L 
— 
4.0 
2.47 
+ L 
+L 
+M 

1.70 
_ 
_ 
_ 
.5 
1.76 
+ M 
_ 
— 
1.0 
1.84 
+ M 
+s 
— 
2.0 
2.00 
+ L 
+ L 
— 
3.0 
2.20 
+ L 
+ L 
— 
3.4 
2.25 
+ L 
+ L 
— 
3.5 
2.26 
+ L 
+ L 
+few VS 
4.0 
2.31 
+ L 
+ L 
+few L 
1 See footnote under Table 1. 
In order to determine the relation between the number of acid- 
forming bacteria, the acidity, and the alcohol test, two experiments 
were performed, using a pure culture of a lactic-acid-producing organ- 
ism. The culture was inoculated into sterile skim milk and incubated 
at 37° C. A bacterial count was made while the acidity and the 
alcohol test were determined at the same time. From the results 
shown in Table 4 it may be seen that in Experiment I the alcohol 
test was negative even after seven hours of incubation. At that time 
