178 CELLS, DIRT AND DEBRIS 



heating of the diluted milk tubes to 70° in Savage's method 

 before centrifugalising would possibly produce higher results. 



In 1910 Prescott and Breed ^^ suggested the examination of 

 the milk directly by means of stained smears. They found the 

 results obtained by this method to be very much higher than 

 by the Doane-Buckley method and that they were also more 

 consistent. This was due to the varying number of cells 

 trapped by the rising fat globules. Breed afterwards devel- 

 oped the process given on p. 129 which is obviously as applicable 

 to cell examination as to the enumeration of bacteria. As 

 previously mentioned, the accuracy of this method depends 

 upan the even distribution of the cells and, if this condition 

 does not obtain, a very large number of fields must be examined 

 in order to obtain a fair average. With a cell count over 500,000 

 per c.cm. the author has obtained good results with this method 

 but for smaller counts the method of Savage is to be preferred 

 on account of the factor for the conversion of the ceUs per field 

 to cells per unit volume being so much smaller. 



Significance. Despite the numerous investigations that 

 have been made in Europe and America during the last seven- 

 teen years, the significance to be attached to presence of cells 

 in milk is still surrounded with difficulties. It has already 

 been pointed out that a large number of cells are to be expected 

 in the secretion of such an active organ as the udder even under 

 normal physiological conditions and that stimulus, whether 

 mechanical or pathological, results in an increase in numbers. 

 As might be anticipated under such conditions the difiiculty 

 lies in estabhshing what might fairly be regarded as the normal 

 variation in the number of cells. Savage found variations 

 ranging from 50,000 to 1,000,000 cells per c.cm. Russell and 

 Hoffmann found counts as high as 1,800,000 in animals in which 

 there was no history of clinical disease while 33 per cent of the 

 samples contained over 500,000 cells per c.cm. Stone and 

 Sprague,^^ using the Doane-Buckley method, examined two 

 healthy cows during the whole milking period (1,167 samples) 

 with the following results: 



