IOS MILK 



To isolate the streptococci, brush diluted loopfuls of the 

 positive tubes over plates containing nutrient agar. Incubate 

 for 24 hours, and if necessary for 2 days, at 37 C. Subcultivate 

 the colonies with the characters of streptococcus colonies into 

 broth or upon sloped agar in tubes containing condensation water. 

 In cases in which streptococci are likely to be scanty, part of the 

 centrifugalised deposit may be used to inoculate the agar plates. 



The tests recommended to differentiate the streptococcus 

 strains isolated are the following : morphology, growth upon 

 sloped nutrient agar, growth in nutrient broth, growth upon 

 gelatine slope, action upon litmus milk, the production of acid in 

 lactose, saccharose, salicin, mannite, raffinose, and inulin. 



The sugar-alcohol media for the differentiation of strepto- 

 cocci were introduced by Gordon. Their method of preparation 

 is given in the Appendix. 



For some purposes it is of great value to ascertain the patho- 

 genicity of isolated strains of streptococci. This is conveniently 

 done by injecting mice subcutaneously or intraperitoneally. 



The presence or absence of streptococci in milk may also be 

 studied by a careful examination of the centrifugalised deposit 

 stained by methylene blue. Failure to find streptococcus chains 

 does not mean they are absent, but only suggests they are not 

 present in considerable numbers. The stained deposits from 

 samples of vended milk, usually show numerous streptococci, 

 but in those made from fresh byre milk samples they are as a 

 rule not to be demonstrated. 



Comparative value of above methods, 



The estimation of the cellular content is of great value in the 

 examination of the milk of individual cows. Cellular elements 

 are invariably present in milk even from perfectly healthy cows 

 but as a rule not in large numbers. Numbers varying from 

 50 to over 1000 per cubic mm. have been recorded by the writer 

 from the milk of individual healthy cows. Any considerable 

 increase is due to physiological or pathological changes (old 

 or recent) in connection with the udder or teats. 



Examples of physiological conditions are advanced pregnancy 

 or the first few days after calving. Pathological causes are any 



