8 BULLETIN 202, TJ. S. DEPARTMENT OF AGRICULTURE. 



alcohol test and the acidity of milk. Rammstedt (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 



acid added 



to 50 c. c. 



of milk. 



Acidity. 



Alcohol test. 



75 per cent. 



68 per cent. 



44 per cent. 



c. c. 





 0.5 

 1.0 

 3.0 

 3.5 

 4.0 





 .5 

 1.0 

 2.0 

 3.0 

 3.4 

 3.5 

 4.0 



1.81 

 1.88 

 1.94 

 2.21 

 2.38 

 2.47 

 1.70 

 1.76 

 1.84 

 2.00 

 2.20 

 2.25 

 2.26 

 2.31 



i + M 

 + L 

 + L 

 + L 



+ M 

 +M 

 + L 

 + L 

 + L 

 + L 

 + L 



+M 

 + L 

 + L 

 +L 



+s 



+ L 

 + L 

 + L 

 + L 

 + L 



+ M 



+few VS 

 +few L 



1 See footnote under Talile 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 



