86 Report of the Department of Bacteriology of the 



RESULTS. 



The milk from thirty-seven dairy farms was examined. The 

 conclusions, however, as to the comparative value of the two methods 

 of counting bacteria were based largely on the results obtained from 

 four of these, which were designated as Farms A, B, C and D, 

 respectively. Examinations were made of the milk from these farms 

 over rather long periods of time, considerable care and attention 

 being given to the counting of many microscopic fields in each sample. 

 Not more than one week was devoted to the study of each of the 

 remaining thirty-three dairies and never more than five microscopic 

 fields were counted in any sample in estimating the number of 

 bacteria present. This latter work was more in the nature of a 

 general survey, and was done with a view of determining the 

 efficiency of the method where used rapidly, as it would be under 

 commercial conditions. 



The milk was delivered by the producers in 40-quart cans previously 

 washed and steamed at the milk stations. The morning milk was 

 from five to six hours old by the time the smearing and plating 

 were done, while night milk was from fifteen to sixteen hours old. 

 The following results show the bacterial content of the milk as it 

 was delivered at the milk station, and are interesting from this 

 point of view as well as from that of this bulletin. 



Table I contains the results of comparative counts made by the 

 two methods on seventy samples of morning milk from Farm A. 

 The microscopic count is subdivided into three columns: The first 

 shows the total number of individual bacteria per cubic centimeter, 

 counting each bacterium seen. The second column shows the 

 totals obtained when clumps and isolated bacteria were each counted 

 as single objects. This kind of a count was made because it is 

 generally assumed that a colony on a petri plate may originate 

 either from a single organism or from a clump. The third column 

 shows the number of clumps found per cubic centimeter. The 

 last column gives the ratios between the counts given by the plate 

 method and the counts given in the first two columns showing the 

 results obtained by the microscopic method. 



Individual cocci in diplococcus or streptococcus chains, and rod 

 forms where the plane of division showed clearly were counted as 



