TRANSPORTATION PROBLEMS. 175 



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 is 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 positively 

 known by experiment, inasmuch as we do not know the actual 

 cause of the diseases. But the practical experience of physicians 

 tells 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 are 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. 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 dependent 

 upon the rapidity of the stream flowing through. These are called 

 continuous pasteurizers. Generally speaking, this type is apt to 

 be less efficient than the discontinuous pasteurizers, and are more 

 subject to irregularity. Either type is efficient if properly managed, 

 but carelessness and haste on the part of the employees may render 

 either kind unreliable and inefficient. 



In the last few years the plan of pasteurizing the milk on a large 

 scale has come to be frequently adopted. It is done in creameries 

 in connection with butter-making, and in some of our large cities 

 for the treatment of the general milk-supply. In the pasteuriza- 

 tion of the public milk-supply the purpose has not been, primarily, to 



