376 PUBLIC HEALTH BACTERIOLOGY 

 BUTTER. 



Butter is made from the cream of milk by churning or 

 agitation, whereby the globules of fat are broken, or 

 rather have their casein envelopes ruptured, and then the 

 fat globules adhere. The cream is first allowed to sour, 

 otherwise the butter will be flavourless. The souring 

 isjbrought about by bacteria, nearly all of which are lactic 

 acid formers. Tuberculosis is the only infective disease 

 transmitted by butter. Tubercle bacilli have been found 

 alive and virulent in butter after having been kept in a 

 refrigerator for five months. Rabinowitch's acid-fast butter 

 bacillus is easily distinguished culturally from the tubercle 

 bacillus. Foot and mouth disease has been reported as 

 having been transmitted by butter. Typhoid infection 

 is unlikely, and has not yet been definitely traced. 



CHEESE. 



Cheese is the precipitated casein of milk, the casein 

 or curd being insoluble. In hard cheeses the whey is 

 better expressed than in soft cheeses, and so the sub- 

 sequent " ripening " which is due to bacterial growth is 

 less in the former than in the latter. In the ripening of the 

 curd, three groups of bacteria are engaged, (i) acid pro- 

 ducers, like B. acidi lactici, (2) casein digesters, which break 

 down the curd, and (3) gas producers, which honeycomb it. 

 The actual organisms engaged have been determined in the 

 case of particular cheeses, and are : a bacillus resembling 

 the Bacillus subtilis, a mould (Oidium lactis), a penicillium 

 mould, and yeasts. Tubercle bacilli of the bovine and 

 human types have been found in cheeses. 



SHELLFISH. 



For Houston's methods, see Journal of Hygiene, vol. iv, 

 No. 2, p. 185. 



WATERCRESS AND OTHER VEGETABLES. 

 See Report to the L.C.C., by Houston, 1905. 



