148 CITY MILK SUPPLY 



She examined the milk of five herds of cows stabled in modern clean 

 barns; three herds were in the vicinity of Washington, D. C., and two sup- 

 plied certified milk to Chicago. Special methods of isolating and study- 

 ing the bacteria were developed. In all, 192 samples of milk from 161 

 cows were examined. The intention was to consider only cultures which 

 were capable of multiplying in the udder and becoming localized there 

 and so no attention was given to types which occurred in small numbers. 

 Altogether 32, or 16.1 per cent., of the 192 samples were from quarters of 

 the udder in which the bacteria were not multiplying in numbers worth 

 considering. Three types of microbes, viz., streptococci, staphylococci 

 and bacteria were found. 



In studying the streptococci a most important distinction was made 

 between two groups, namely: (1) the long-chained streptococci which 

 curdle litmus milk and partially decolorize it thereafter; and (2) St. 

 lacticus which, prior to curdling, produces complete decolorization be- 

 neath a pink layer. St. lacticus was not found in any of the samples 

 of milk which indicates that it does not localize and multiply in the 

 udder. The long-chained streptococci were isolated from 29, or 15.1 

 per cent., of the whole number of samples. The highest number found 

 per cubic centimeter was 264,000. 



The micrococci were the most frequent components of the udder flora; 

 they were found in 113, or 58.8 per cent., of the whole number of samples, 

 the highest .number per cubic centimeter being 80,000. The majority 

 of the micrococci belonged to a single group which agrees with the pyo- 

 genic staphylococci. The majority of the cultures of this group were non- 

 virulent but two were highly virulent to rabbits. To a second group no 

 name was given because of the small numbers of cultures studied. A third 

 group was identified with M. luteus. A fourth group was characterized 

 by rapid and complete peptonization of the milk; hence it was named 

 M. caseolyticus. 



Bacteria of peculiar strains of types commonly present in freshly 

 drawn milk, were sometimes found localized in the udder of several cows 

 of one dairy and a few cases were found of peculiar species, unlike any of 

 the udder organisms, being localized in the udders of several cows of one 

 dairy. The Bacilli commonly present in milk from all dairies were shown 

 to be related to Bad. abortus. Three varieties of this type were distin- 

 guished. The variety of Bad* abortus occurring most frequently in the 

 samples 0f milk was designated Bact. abortus, var. lipolyticus because it 

 decomposes butterf at ; it agrees closely in its culture characteristics with 

 Bang's original description, of Bact. abortus. Cultures of this variety 

 were shown to be capable of imparting undesirable flavors and odors to 

 cream kept under conditions such as those to which it often is subjected. 

 Other varieties of the Bact. abortus type differed considerably^ from the 

 lipolyticus variety but resembled cultures isolated from pathogenic 



