PATHOGENIC BACTERIA IN BUTTER AND CHEESE 307 



were still virulent, but it seemed possible, judging from the 

 gradual decrease in virulence, that they might have died out by 

 the end of four months. 



Heim believed that tubercle bacilli died after about four weeks 

 in cheese. Galtier, however, found that they were still virulent 

 after about seventy days. 



Mohler, Washburn, and Rogers, investigating the presence of 

 tubercle bacilli which had been added to milk and subsequently 

 made into cheese, considered that there was some reason to suppose 

 that tubercle bacilli might die out after four months, but possibly 

 a longer period might be required. 



Evidently the longevity of tubercle bacilli in cheese becomes 

 important if the cheese is to be consumed within the period over 

 which they are known to be virulent. Some cheeses take several 

 months to ripen, but many are eaten considerably within four 

 months after their manufacture has commenced. 



Difficulties have been experienced in manufacturing cheese 

 from milk which has been pasteurised, but these appear to have 

 been now largely overcome. Thus Liska, dealing with the manu- 

 facture of cheese from pasteurised milk, used milk which had been 

 heated to 65 68 C. He commenced using heated milk on 

 account of an outbreak of foot-and-mouth disease in the district, 

 and also apparently because the fodder given to the cattle in that 

 district (and utilised both for economy and for general convenience) 

 appeared to produce a milk containing many organisms and having 

 a peculiar taste. (Note. The methods of collecting the milk are 

 not given, but it seems probable that the bacteria were derived 

 from the faeces of the cow. The fodder used was a particular 

 waste from breweries which is well known to produce very liquid 

 faeces, and unless the strictest cleanliness is exercised the faecal 

 material which clings to the cow will almost certainly fall into 

 the milk.) 



Liska kept the temperature at the above-mentioned point for 

 from twenty-five to thirty minutes ; the milk was then cooled to 

 the proper temperature for the addition of rennet. The results 

 obtained appear to have been successful, and Liska notes that 

 killing the B. Coli before utilising the milk for cheese produces a 

 firmer cheese with fewer holes than that produced when B. Coli 

 is present. 



Sammis and Brahny, working in America, found that the addition 

 of hydrochloric acid up to 0-25 per cent, restores the property of 

 clotting to pasteurised milk and improves the flavour. They 

 experimented for many years in the making of cheese with milk 

 which had been pasteurised at a temperature of 160-165 F. 

 If the temperature is raised much above this point, the quality 

 of the cheese is stated to be affected. The authors found that 

 clotting was more readily produced in the pasteurised milk by the 

 addition of acid, than by the addition of a calcium salt, which, as 



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