METHODS OF EXAMINING MILK 273 



that the milk under examination contains the secretion of 

 a cow affected with catarrhal mastitis. 



If the plates prepared from a sample of herd milk 

 contain a large number of extremely minute brownish 

 colonies, which upon microscopic examination are found 

 to consist of streptococci in rather long chains, an ex- 

 amination of the herd from which the milk came will re- 

 sult in the discovery of one or more cows affected with 

 catarrhal mastitis. To examine microscopically, place one 

 of the colonies in a drop of water on a glass slide and 

 spread by a gentle rotary motion of the platinum nee- 

 dle, beginning at the centre and working outward; dry, 

 fix by heat and stain with methylene blue. The chains 

 of Streptococcus lacticus are shorter than those of the 

 streptococci of mastitis, rarely containing more than 6 or 

 8 cocci, and the individual cocci are arranged as diplo- 

 cocci. (See Figs. 5 and 6.) 



The method of examination for streptococci recom- 

 mended by the Laboratory Section of the American 

 Public Health Association is as follows : 



" Where streptococci, diplococci, or cocci are found in 

 the sediment, and the plate from the same sample con- 

 tains colonies resembling streptococci colonies, these colo- 

 nies may be grown in bouillon to see if chains will develop. 



"First make and record an estimate of the number of 

 such colonies present, then transfer from 10 to 50 of them 

 to bouillon and grow for 15 to 24 hours at 37 C. To ex- 

 amine the bouillon culture, spread a loopful on a glass 

 slide, fix with heat, fix with alcohol while slide is still quite 

 hot, stain with methylene blue, wash immediately, dry 

 and examine. 



"A milk should not be condemned because a few 

 chains are found together with large numbers of other 

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