188 CONTROL OF THE MILK SUPPLY 
The value of pasteurization is becoming rapidly recognized, and 
this method of treatment is being widely adopted. The ad- 
vantages lie in the following facts: 
1. It produces milk which cannot be distinguished from fresh 
milk and will be used as freely. 
2. It increases the keeping property of the milk, but not to the 
extent of leading the consumer to believe he can keep it indefinitely, 
The consumer is thus forced to use it up before the spore-bearing 
bacteria get an opportunity of multiplying sufficiently to produce 
the injurious secretions which occasionally render sterilized milk 
dangerous. The very fact that the method does not destroy all 
bacteria 1s a safeguard. 
3. It removes the danger of distributing pathogenic bacteria. 
This is certainly quite true of the typical diseases mentioned. 
Whether it similarly removes the danger of diarrheal diseases, 
not dependent upon any known specific bacteria, is not yet posi- 
tively known by experiment, inasmuch as we do not know the 
actual cause of the diseases. But the practical experience of 
physicians tclls us that pasteurized milk acts as efficiently as 
sterilized milk in reducing these diseases. 
4. This method of treatment is perfectly applicable upon a 
large scale. Several forms of apparatus have been devised that 
accomplish the end rapidly and upon large quantities of milk. 
Of these, there arc two general types. In one a large quantity of 
milk is heated to the desired temperature and maintained at this 
temperature as long as desired, after which it is cooled. These 
are called discontinuous pasteurizers. Popularly the method is 
known as the “‘holder’’ process. In the other type the milk is 
passed through the apparatus in a constant stream, being heated 
and cooled while it passes through. In these machines the milk 
is sometimes only just brought to the desired temperature, and 
cooled at once; and in all cases the extent of the heating is depend- 
ent upon the rapidity of the stream flowing through These are 
called continuous pasteurizers. Popularly this process is called 
