298 MILK AND ITS HYGIENIC RELATIONS 



who possess a wide knowledge of the conditions of the general 

 milk supply, consider that all milk should be pasteurised before 

 being placed on sale, with the possible exception of milk of a high 

 quality which may be specially produced for infants or invalids. 

 Others, again, consider that it is more advisable for the general milk 

 supply to be sold without being heated, unless a statement is made 

 to the effect that heat has been applied to the milk before sale. 

 More discussion appears to have arisen in connection with the 

 pasteurisation of the general milk supply in America, than in any 

 other country. The advances which have been made in the United 

 States in the production of ' certified ' milk have led to a close 

 investigation of the general milk supply. 1 Where the general 

 milk supply is under consideration it is contemplated that pasteur- 

 isation shall take place as soon as possible after milking. The ob- 

 ject of pasteurisation is, first, to remove any possible pathogenic 

 bacteria which may be present, and, secondly, to preserve the milk 

 for a longer period than would be the case if it were not heated. 

 The preservation of the milk is perhaps more necessary in America 

 than in this country. The milk has frequently to travel very long 

 distances before it reaches the city in which it will be distributed. 

 In the summer-time the heat is greater than in this country, although 

 this adverse condition for the preservation of milk is to some extent, 

 if not entirely, modified by the use of refrigerating wagons by the 

 railway companies. Hence the milk, if it is placed on the train 

 cool, does not become heated on the journey. The approximate 

 duration of time which must elapse between milking and the dis- 

 tribution of the milk is known to be considerable, and the milk is 

 pasteurised in order to preserve it for this period. 



In many districts in America large pasteurising plants have 

 been established, and the milk is brought to the pasteurising station 

 from a number of farms in the surrounding district. The milk 

 is then subjected to pasteurisation on a vast scale, being subse- 

 quently despatched from the centre to the train, and to the town 

 for which it is destined. Milk which has been pasteurised under 

 this system must be sold as pasteurised milk, and may be further 

 sold in grades of milk. 8 In America the lower grades of milk 

 are not usually regarded as being suitable for infants' food, but 

 for ordinary household or cooking purposes only. 



In this country pasteurisation, when used by dairymen, appears 

 for the most part to be carried out on a relatively small scale by 

 the individual dairyman, and to be used for the purpose of preserving 

 milk which has not been sold on one day until the next day. That 

 is to say, the milk is already somewhat stale and is heated in order 

 to prevent it going sour before it can be sold. 



Two main processes are employed for the pasteurisation of 

 milk and are known respectively as the ' holder process ' and the 



1 Notes upon the standards set by New York City will be found in 

 Appendix G. * Cp. Appendix G. 



