MILK-BORNE INFECTIONS 465 



then adjusted by means of the draw-tube to equal 0.16 mm. 

 Each field then represents 0.005 sq. cm., and each cell seen is 

 equal to 500,000 per cubic centimeter of the sample. For accu- 

 rate work a hundred fields should be counted. For routine work 

 a lower power can be used and a smaller number of fields counted. 



The method of Prescott and Breed has thrown considerable 

 light on the significance of cellular elements in milk. The authors 

 have shown that by centrifuging milk the number of cells thrown 

 into the sediment may be all the way from one-fortieth to one- 

 half of the actual number present in milk. The balance rise with 

 the cream, except a relatively small number which remain on the 

 surface of the sediment and just below the lower line of the cream. 

 Consequently, the number of cells in the sediment is so variable 

 that no reliable estimate can be made. By the new method the 

 cells are evenly distributed and enumeration is fairly accurate. 



Sanitarians have placed faith in certain maximum numbers 

 permissible. With the evolution of better methods the standards 

 have been raised from time to time. Now Prescott and Breed 

 report finding 10,690,000 cells per cubic centimeter in a milk of 

 apparently normal condition. 



In a later paper Breed amplified on the sanitary significance 

 of cellular elements in milk. It is known that milk under some 

 conditions, aside from mastitis, contains large numbers of cells. 

 Colostrum milk and milk during the last weeks of lactation, as 

 stated before, contain exceedingly large numbers of cells. It is 

 quite natural, therefore, that examination of a herd will show 

 some members present which are in initial or terminal stages of 

 lactation, or individuals that are suffering from actual disease. It 

 is not surprising when a relatively high leukocyte count has been 

 the cause of investigation that some abnormal milk is actually 

 found, since some abnormal milk, in small quantity at least, is 

 produced by almost every herd. Breed has found the number of 

 cells in normal milk to be variable even in the milk from different 

 quadrants of the same udder. The largest number is found in 

 the strippings. The same author found 54,300,000 cells in the 

 strippings of an apparently normal cow, and stated that no ill 

 consequences followed consumption of this milk. In the milk of 

 122 cows in apparently normal condition he found 49 per cent, 

 with less than 500,000 cells per cubic centimeter, 29 per cent, 

 with 500,000 to 1,000,000, and 22 per cent, over 1,000,000. The 

 author states further that with the data available there is no rela- 

 tion traceable between the high number of cells and streptococcus 

 infections of the udder; other pathologic conditions; colostral milk; 

 milk from the terminal period of lactation, and certain temporary 

 abnormal conditions of the cow. 



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