PRESERVATION OF MILK 373 



bacteria or their spores. As used in the milk trade 

 " sterilised milk " means mi\k which has been heated to a 

 temperature which it is hoped has killed the bacteria present. 

 Like so many trade expressions it does not mean what it says, 

 or if it purports to mean it, it is not true. 



Baoteriologically sterile milk can be obtained, indeed it is 

 obtained every day in the bacteriological laboratory, but to 

 obtain it means either heating the milk to a temperature 

 above boiling-point sufficient to kill all spores within the time 

 of exposure, or keeping it at 100° C. for short periods on several 

 successive days. Neither of these procedures is applicable for 

 trade purposes since the appearance and taste of the milk are 

 thereby adversely affected. Indeed, the man who would sterilise 

 milk commercially has a difficult problem to solve, since the 

 heat which is to kill the bacterial life must yet be insufficient 

 to alter materially the taste and appearance of the milk.^ The 

 latter usually is attained at the expense of the former, and 

 " sterilised milk " which is sterile is a rarity. This fact has 

 been demonstrated by a number of investigators who have 

 studied commercial " sterilised milk." Tor example, Fliigge's ^ 

 work led him to the conclusion that most of the so-called 

 sterilised milk on the market was not sterile. He divided the 

 bacteria isolated by him into three groups ; and to one group, 

 which he called the peptonising bacilli, he ascribed prejudicial 

 effects, since they caused diarrhoea when fed in milk to young 

 dogs, and were pathogenic to mice, guinea-pigs, and rabbits 

 when injected subcutaneously or intraperitoneally. His results 

 as to the pathogenic properties of these heat-resisting organisms 

 have not been confirmed by other investigators. 



Weber ^ examined 150 samples of sterilised milk from 

 Berlin shops and found only 54 per cent sterile. Although 

 he isolated and described eighteen species of " peptonising " 

 bacilli he could not confirm Fliigge's feeding experiments, and 

 only considered this group as possibly harmful by setting up 

 fermentative changes in the milk. 



^ His problem is analogous to that of the manager of a sewage farm who has 

 to treat the sewage on the land to purify it, while at the same time he is 

 supposed to farm the land profitably and take off good crops. Subordination 

 of the sanitary to the commercial usually results in both cases. 



2 Zeit.f. Hygiene, 1894, voL xvii. p. 272. 



^ Arbeit, a. d. Kaiserl. Gesundheitsamte, 1900, vol. xvii. 



