72 THE BACTERIOLOGICAL EXAMINATION OF MILK 



The difficulties of bacteriological examination of such an article 

 as colostrum are considerable. At the outset, a fair sample is only 

 obtainable by adopting the following precautions : {a) the teats and 

 udder to be cleansed ; {b) milking to be carried out as soon after 

 calving as possible, when the calf has sucked ; {c) the first part of 

 the "milking" to be discarded, and the last part only to be 

 examined. When the colostrum reaches the laboratory it must be 

 diluted in precisely the same manner as thick cream. After 

 abundant dilution treat the solution in the ordinary way, by 

 staining preparations for the microscope, plating out on various 

 media, and subculturing. 



Bacteriologrical examination of butter- 

 Take a quarter of a pound of butter and place it in a sterilised 

 flask with 150 c.c. of sterile salt solution. Place the flask in the 

 water bath at about 35° C, and shake gently until the butter has 

 melted. The contents of the flask now appear as a milk-like 

 emulsion. A small quantity of this mixture may be used for 

 plate cultivation on gelatine and agar, as in milk. The remainder 

 should be placed in a sedimentation flask in the refrigerator for 

 twenty-four hours. By this means the particulate matter of the 

 butter, including the contained organisms, are deposited. After 

 removing the superficial solidified fat by means of a sterile 

 spatula, the turbid fluid may be decanted, and the sediment 

 collected for microscopical examination or the injection of guinea- 

 pigs. {See p. 70, also Inoculation of Animals, p. 74.) 



Examination of cheese— 



With a knife previously sterilised by passing through the 

 flame, cut off from the piece of cheese under examination a thin 

 slice parallel to the surface. Remove this, and with a second 

 sterile knife cut perpendicularly downward from the bared surface, 

 Pass down into the latter cut a coarse sterile platinum needle 

 of which a small portion near the extremity has been slightly 

 roughened with a file. 



Inoculate with this needle a sufficient number of tubes o 

 bouillon, from which plate cultivations can subsequently be made 

 for isolation purposes, and placed under both aerobic and anaerobic 

 conditions. 



Examination of moulds — 



The examination of hyphomycetes or mould fungi is, for differ- 

 entiation purposes, best carried out on the Petri dish itself, where 



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