New York Agricultural Experiment Station. 103 



microscopic field was seen. Since these large, compact, uncountable 

 clumps do not appear to be common in milk they are, practically, 

 negligible. In spite of the uncertainty in the plate counts intro- 

 duced by the clumps it is interesting to note that there appears 

 to be a fair degree of relationship between the two counts in a great 

 number of samples, sufficiently close at least to establish a relationship 

 between the two methods when long series of counts are compared. 



In discussing the irregularities which occur between the two 

 counts the question of dead bacteria must be considered. There 

 is little reason for believing that there are many dead organisms 

 present in fresh, unpasteurized milk excepting possibly some udder 

 species which die off at low temperatures. These are so few in 

 number as to be of no consequence. This fact is substantiated by 

 the results obtained. Moreover, it is well understood that normal 

 fresh milk is such a favorable medium for bacterial life that practically 

 all bacteria thrive in it, or at least exist in an inactive state until 

 so many are present that overcrowding occurs. Then, of course, 

 many are killed. As previously stated, none of the samples taken 

 were more than fifteen hours old and therefore all may be regarded 

 as fresh milk. Where market milk is produced under variable 

 conditions and is continually subjected to contamination, it might 

 occasionally become inoculated with bacteria which do not grow 

 well in milk. In such cases there might be enough dead bacteria 

 to cause appreciable variations between the counts obtained by the 

 two methods, but this would be rare. This might be what actually 

 happened in the sample taken on February 19 (Table II). There 

 is no proof, however, that this is the explanation of this particular 

 discrepancy between the two counts. This much can be said, that 

 the microscopic method shows more accurately the total number 

 of living and dead bacteria present in all samples. The number of 

 bacteria, whether dead or alive, is indicative of the past history of 

 a given sample of milk and of the danger of contamination to which 

 milk has been exposed. 



It is known that dead bacteria do not stain as well as living ones 

 and that they soon disappear as stainable objects. The exact 

 effect which the dead bacteria in pasteurized milk would have upon 

 the microscopic count, or how efficiently the microscopic method 

 would determine the bacterial quality of pasteurized milk, is as yet 

 unknown. 



