CHAPTEE VII 



BACTERIA IN MILK AND MILK PRODUCTS 



General Principles — Sources of Pollution— Number of Bacteria in Milk — Influence 

 of Time and Temperature — Species of Bacteria found in Milk— Fermentations 

 of Milk — Pathogenic Organisms in Milk — Milk-borne Disease : Tuberculosis, 

 Typhoid Fever, Scarlet Fever, Sore-Throat lUnesses, Cholera, Epidemic 

 Diarrhoea — Preventive Measures — Protection of Milk Supply — Control of 

 Milk Supply : Refrigeration, Straining, Sterilisation, Pasteurisation — Special- 

 ised Milk — Bacteria in Milk Products— Cream-Ripening — Butter-Making — 

 Cheese-Making — Abnormal Cheese-Ripening — Poisonous Cheese. 



Injurious micro-organisms in foods are, fortunately for the con- 

 sumers, usually killed by cooking. Vast numbers are, as far as we 

 know, of no harm whatever. Alarming reports of the large numbers 

 of bacteria which are contained in this or that food are generally as 

 irrelevant as they are incorrect. Bacteria, as we have seen, are 

 ubiquitous. In food we have abundance of the chief thing necessary 

 to their life and multiplication — favourable nutriment. Hence we 

 should expect to find in uncooked or stale food an ample supply of 

 saprophytic bacteria. There is much wholesome truth in the 

 assertion that good food as well as bad frequently contains large 

 numbers of bacteria, and often of the same species. It is well that 

 we should become familiarised with this idea, for its accuracy cannot 

 be doubted, and its acceptance at the present time may not be with- 

 out beneficial effect. 



Nevertheless, it is well we should know the bacterial flora of 

 good and bad foods, for at least two reasons. First, there is no doubt 

 whatever that a considerable number of cases of poisoning can be 

 traced every year to food containing harmful bacteria or their products. 

 To several of the more illustrative cases we shall have occasion to 

 refer in passing. Secondly, we may approach the study of the 

 bacteriology of foods with some hope that therein light will be found 



