PRESERVATION OF MILK 383 



days. Old, stale milk may be sold as fresh, owing to the 

 removal of most of the lactic acid bacilli. Such milk will 

 appear normal to sight and taste, but may be bacterially 

 highly dangerous. 



(5) If used without statutory control, there can be but 

 little doubt that the extensive use of pasteurisation would 

 lead to neglect of general sanitary precautions even more com- 

 pletely than is the case to-day, under the belief that the 

 pasteurisation would be an efficient substitute for cleanliness. 



(6) The pasteurisation may, by altering its chemical and 

 physical composition, damage the milk as a commercial article 

 and diminish its digestive and nutritive properties. The 

 extent to which such changes take place will depend upon the 

 temperature of pasteurisation. At 60° C. the milk appears to 

 be physically or chemically unaffected. At 71° C. the milk is 

 affected, and the cream will not rise properly. The influence 

 of cooking milk upon its utility in infant feeding has been 

 already discussed. Unless the pasteurisation temperature is a 

 high one, there is probably no great objection to the process 

 on this ground. 



It is probable that much commercial pasteurisation is 

 inefficiently done. It is a procedure involving an accurate 

 adjustment of time and temperature, and frequently being left 

 to be performed by careless and unskilled persons (the so-called 

 " practical man ") it is very unequally and inefficiently done. 

 If pastem'isation is to be allowed at all, it should be controlled 

 both as regards methods and apparatus. 



In the writer's opinion, summing up the matter, pasteur- 

 isation is an efficient and useful procedure, which may be 

 very valuable pending satisfactory and radical improvement in 

 the milk business as a whole, but it is likely to be more 

 harmful than beneficial unless the practice is rigidly supervised 

 and the conditions under which it may be employed regulated. 



IV. Chemical Preservatives 



Chemical preservatives are added to milk to retard or 

 prevent bacterial growth, so that the milk will keep in an 

 apparently unaltered condition for a period considerably 

 longer than if they were absent. The substances which have' 



