Preservation of Milk. 129 



order to secure satisfactory results on the bacterial content 

 of the cream. 



Tests Of apparatus. But few of the continuous-flow 

 type of machines have been subjected to rigid bacterio- 

 logical control, and their efficiency is questionable. By 

 their use it may be possible to enhance the keeping qual- 

 ity of milk in a fairly satisfactory way, and yet not in- 

 sure complete freedom from disease-producing bacteria. 

 One grave defect in many of them is that all parts of the 

 milk are not heated uniformly. It is easily possible for one 

 part to be over-heated while the remainder is under-heated; 

 and while the outlet may show a suitable temperature, still 

 it does not follow that all parts of the milk have been 

 thoroughly treated. 



The following simple method enables the factory operator 

 to test the period of exposure in the machine: Start the 

 machine full of water, and after the same has become heated 

 to the proper temperature, change the inflow to full-cream 

 milk, continuing at the same rate. Note the exact time of 

 change and also when first evidence .of milkiness begins to 

 appear at outflow. If samples are taken from first appear- 

 ance of milky condition and thereafter at definite intervals 

 for several minutes, it is possible, by determining the amount 

 of butter-fat in the same, to calculate with exactness how 

 long it takes for the milk to entirely replace the water. 



Intermittent pasteurizers. Inasmuch as the biological 

 and physical requirements of successful pasteurizing neces- 

 sitate milk being heated between the temperatures of 

 140 and 160 F., it is desirable that the temperature should 

 also be under complete control. Moreover, the treatment 

 should also be in such a way as absolutely to insure all the 

 milk being treated for a given period of time. A fulfill- 

 9 



