438 CITY MILK SUPPLY 



deeply stained, excepting the thick portions, than the unheated milk and 

 the leukocytes take the stain more deeply than the background so that 

 they appear as dark blue areas in a light blue field. Often there is a 

 halo about the leukocytes owing to the background immediately sur- 

 rounding them staining deeply and shading off into the general color of 

 the smear. The oil immersion lens shows the polymorphonuclear cells 

 readily, with less irregular outline than those of the raw milk and shrunken 

 to about ?M in diameter. The nuclei are distinctly stained. The amount 

 of the shrinking and the depth of the stain vary some with the degree of 

 heat applied. The shrinking of the cells begins at a lower temperature 

 than that used for pasteurization and their shape gradually changes as 

 the degrees of heat increase. The fixing of the nuclear material which 

 makes possible the absorption of the stain seems to take place at between 

 140 and 145F., the temperature used in the holder process of pasteuriza- 

 tion. The changes Frost points out as characteristic of heated milk are 

 observable in the Stewart-Slack smears, so those that use them say, and 

 they hold that the smears may be used for detecting heated milk. 



The Bacteria Count. It is but recently that the bacterial content 'of 

 milk has been used as a criterion of milk quality. The first bacterial 

 count of a municipal milk supply to be published in the United States 

 were those of Sedgwick and Batchelder who in 1892 gave out the results 

 of their study of the milk of Boston. At about the same time Conn 

 published the counts he obtained in investigating the milk supply of 

 Middletown, Conn. Other bacteriologists took up the work and before 

 long many cities were making regular bacteriological examinations of the 

 milk served the public. Montclair, N. J., was the first municipality to 

 regularly publish the results of such examinations. There the effect was 

 that the public became interested at once and began to favor those dealers 

 whose milk had low counts. Soon cities began to establish bacteriological 

 milk standards. Thus New York City in 1900 adopted a maximum 

 limit of 1,000,000 bacteria per cubic centimeter and Boston a little later 

 established a limit of 500,000 bacteria per cubic centimeter. Other 

 cities followed so that in 1914 the U. S. Public Health Service was able 

 to publish a list of 149 cities, each having a population of over 10,000 and 

 having together a population of somewhat over 21 million, that had set 

 up bacteriological standards of some sort. 



There is no question but that the bacterial count has been very 

 effective in improving many milk supplies. The result of publishing 

 counts has been to focus public attention on clean methods of milk 

 production and on the proper care of the milk and this has reacted on 

 producers and dealers, making them emulate the methods of the best 

 dairymen. Notwithstanding this, some bacteriologists question the 

 wisdom of laying great stress on the bacterial count on the ground that it 

 is inexact and illogical. 



