124 EXPERIMENTAL DAIRY BACTERIOLOGY 



some idea as to the dilutions to be used in the preparation 

 of plate cultures, so as to obtain plates with the desired 

 number of colonies. 



Microscopic examination for streptococci. As has been 

 previously pointed out, the pyogenic organisms most likely 

 to be the cause of udder troubles are streptococci of the 

 type of Streptococcus pyogenes. In the examination of the 

 smears prepared from the milk sediments, the form of organ- 

 isms predominating should be noted. The value of the ex- 

 amination depends much upon the age of the milk. It is 

 impossible to distinguish certain types of lactic-acid organ- 

 isms from pyogenic streptococci, since their morphology is so 

 nearly identical. Thus, in milk, in which the lactic organ- 

 isms have increased in numbers, such an examination is of 

 doubtful- value. In perfectly fresh milk long chains of strep- 

 tococci are indicative of udder trouble. In milk of animals 

 suffering from garget immense numbers of such organisms 

 may frequently be found in the sediment. 





