Testing the Parity of Milk. 129 



fits, holding a certain number of cylindrical glass tubes; these 

 are all numbered and provided with a mark and a tin cover. 

 In making the test, the tubes are filled to the mark with milk, 

 the number of each tube being recorded in a note-book, oppo- 

 site the name of the particular patron whose milk was placed 

 therein. The tubes in the rack are put in the tank, which is 

 two-thirds full of water; the temperature of the water is kept 

 at 104-106 F. for six hours, when the rack is taken out, the 

 tubes gently shaken, and the appearance of the milk, its odor, 

 taste, etc., carefully noted in each case. 



The tubes are then 

 again heated in the tank 

 at the same temperature 

 as before, for another six 

 hours, when observa- 

 tions of the appearance 

 of the milk in each tube 

 are once more taken. 

 The tainted milk may 

 then easily be discov- 

 ered by the abnormal FIG. 47. The Gerber fermentation test, 

 coagulation of the sample. According to Gerber, 1 good and 

 properly handled milk should not coagulate in less than twelve 

 hours, when kept under the conditions described, nor show 

 anything abnormal when coagulated. Milk from sick cows 

 and from cows in heat, or with diseased udders, will always 

 coagulate in less than twelve hours. If the milk does not curdle 

 inside of a day or two, it should be tested for preservatives 

 (290). 



153. The Monrad Rennet test is used by cheese makers 

 for determining the ripeness of milk. Fig. 48 shows the 

 apparatus used in the test. 5 cc. of rennet extract is 

 measured by means of a pipette into a 50 cc. flask 5 the 



i Die praktische Milchpriifung, p. 85. 

 9 



