THE ALCOHOL TEST IN EELATION TO MILK. 33 



alcohol test indicates some change in the milk from its normal con- 

 dition. In our opinion the value of the alcohol test with milk from 

 a single cow or small herd lies in the fact that it would show that the 

 milk was abnormal, and in consequence a careful examination should 

 be made of the herd. 



When the relation of the alcohol test to mixed market milk is dis- 

 cussed, we must consider it on an entirely different basis. In this 

 case the test with 68 per cent alcohol may be positive as a result of 

 changes produced in milk through bacterial action. The results of 

 our work confirm some of the results of other investigators and show 

 that the alcohol test may be positive as a result of the growth in milk 

 of lactic-acid and rennet-forming bacteria. When the growth of 

 these bacteria has reached a point where the acid or rennet is pro- 

 duced in sufficient quantities to affect the casein, a coagulation is 

 produced when equal volumes of 68 per cent alcohol and milk are 

 mixed. Our results, however, do not show that there is any definite 

 relation between the alcohol test and the number of bacteria in milk. 

 During an examination of 177 samples of raw milk we found that 20 

 samples gave a positive test with 68 per cent alcohol. Of these 20 

 samples 8, or 42.1 per cent, contained less than 500,000, and 11, or 

 57.9 per cent, more than 500,000 bacteria per cubic centimeter. It 

 was also found that 39.4 per cent of 142 samples of milk which gave 

 no positive alcohol tests contained over 500,000 bacteria per cubic 

 centimeter. That there is no definite relation is probably explained 

 by the fact that bacteria may increase in large numbers before there 

 is much acid or rennet produced. Consequently, if an alcohol test 

 were made during that period there would be a high bacterial content 

 and yet not enough change produced in the milk by acid or rennet 

 to cause a positive test. Besides this point it must be remembered 

 that in market milk there is a bacterial flora representing many dif- 

 ferent species, many of which may increase without influencing the 

 alcohol test. 



As stated before, generally speaking, when the bacterial fermenta- 

 tions have advanced to a point where chemical changes are produced, 

 the alcohol test will be positive as a result of lactic or rennet fermen- 

 tations, or a mixture of both. In such cases the alizarol test may 

 be of more value than the plain alcohol test, so far as it may give 

 additional information as to the kind of fermentation. From our 

 results it seems evident that the acid-and-rennet fermentations may 

 be differentiated by means of neutralization of the acidity by sodium 

 hydrate. 



The alcohol titration method according to our tests seems to offer 

 no particular advantages over the alcohol test. In a study of 116 

 samples we were not able to find any definite relation between the 

 alcohol titration and the bacterial count. 



