32 



BULLETIN 202, U. S. DEPARTMENT OF AGRICULTURE. 



the alizarol test. Among the other 73 samples of milk, which ac- 

 cording to the alizarol test were normal, there were samples which 

 had a high bacterial content and which were abnormal according to 

 the leucocyte and other tests. From his results Thoni believes that 

 the alizarol test is not sufficiently delicate for use in market-milk 

 investigations. However, he believes the test is of value as a quick 

 means for detecting udder infection in animals. 



It is evident that there is a diversity of opinion as to the value of 

 the alizarol test, and our experiments have not been extensive 

 enough for us to form a definite opinion in regard to it. 



We have tried the test on a number of samples of milk and have 

 not been able to obtain all the color changes which are described by 

 Morres. When the acidity was slightly above normal we found a 

 change from lilac red to pale red and brownish red. In one sample 

 of milk we increased, the acidity by the addition of lactic acid and 

 obtained the colors named below. 



Amount of N/10 lactic 

 added to 50 c. c. of milk. 



Acidity. 



Color of alizarol test. 





1.85 

 2.10 

 2.42 

 2.73 

 3.00 

 5.15 



Lilac red. 

 Pale red. 

 Brownish red. 



Do. 



Do. 



Do. 



2 c. c 





6 c. c 



8 c. c 



1.5 c. e. normal acid. . 



From our results we believe that alizarin will show slight changes 

 in the acidity when the acidity is low, but that the indicator did not 

 seem to be very sensitive to high acidities in milk. Morres (22), in a 

 paper in 1913, also states that alizarin is of greatest value in indi- 

 cating the first changes in acidity and that the color change is so 

 gradual at acidities over 16° that the test is of no particular value. 



In regard to the value of the alizarol test we believe that wherever 

 the alcohol test can be considered of value, the addition of an indi- 

 cator, such as alizarin,, may increase the value of the alcohol test by 

 possibly giving additional information as to acidity. 



On account of the complexity of the bacterial fermentations in 

 market milk we do not believe that the alizarol test gives any very 

 valuable information as to the conditions existing in the milk. 



CONCLUSIONS. 



In conclusion, we wish to point out again that the alcohol test 

 must be considered from two standpoints: First, in its relation to 

 the milk from a single cow or small herd, and, second, in its relation 

 to mixed market milk. 



As to the relation of the alcohol test to milk from a single cow, it 

 seems evident from the work of other investigators, which is con- 

 firmed to some extent by our results, that a positive 68 per cent 



