BACTEEIAL MILK ANALYSIS 253 



A rough test is to place five tubes of the milk to be 

 tested at 20 C., 27 C. and 37^ C., observing time and 

 character of the coagulation and the odor. 



This test does not require extra apparatus, uses but 

 little milk, does not require rennet and in the hands of 

 one familiar with the fermentation of milk gives good 

 results. 



Determination of acidity. While milk is still fresh, 

 i.e., before it has begun to undergo lactic fermentation, 

 it will show an acid reaction which is sometimes ex- 

 pressed in terms of lactic acid. In view of the fact that 

 the acidity of ' l sweet 7 ' milk is due partly to the presence 

 of acid phosphates and partly to dissolved carbonic acid 

 in milk and not to lactic acid, which is probably absent, 

 a better plan is to express the acidity in terms of the 

 number of cubic centimeters of tenth normal alkali 

 necessary to neutralize a given quantity of the milk, 

 either 25 or 50 c.c., using phenolphthalein as an 

 indicator. 



If it is desirable to calculate the acidity in terms of 

 lactic acid, multiply the number of cubic centimeters of 

 tenth normal alkali used by 0.897 and divide by the 

 number of cubic centimeters of milk titrated, the result 

 being the percentage of lactic acid. For all practical 

 purposes the factor 0.9 instead of 0.897 may be used. 

 For field work acidity of milk may be measured quite 

 accurately by the alkaline tablet method. 



Records. A card catalogue is far superior to any 

 other method of keeping records. 



A series of working cards may be kept in order of 

 the date and duplicates entered in another series in 

 order of the place obtained, thus making it easy to refer 

 to any day's work or to any special dairy. 



Cards of different colors may be used to distinguish 

 the different sources, such as samples taken from stores, 

 teams, etc. 



The collector may take cards with him and enter 

 details as he takes his samples, or the sample number 

 may be written on the test tube and the details opposite 

 the same number in a notebook, cards being copied from 

 the notebook on return to the laboratory. 



