902 Popular Editions of Station Bulletins of tiik 



the effect of a change from hand milking to machine milking; and 

 the remainder of the herd furnished 56 samples of hand-drawn milk 

 and twice as many drawn by machine. 



The investigation proves plainly that milk appar- 

 Normal milk ently normal in all respects, from healthy cows in 

 rich in cells, all stages of lactation, milked by hand or by machine, 

 contains large numbers of cells. The average for 

 the Station herd was lower than that of any other herd examined 

 but was still 439,000 per cubic centimeter; the Guernsey herd came 

 next, with 895,000, the three German cows were third, with 932,000; 

 and the Pennsylvania herd averaged over a million cells per cubic 

 centimeter. These numbers are much greater than those reported 

 by other investigators, owing to the greater severity of the method 

 used. By the older methods many cells in centrifuged samples were 

 lost in the cream or remained in the milk and therefore could not 

 be counted in the sediment samples used. It will be noticed that 

 the average number for each of these herds, except that of the Station, 

 is above the limit fixed as an allowable maximum as a result of 

 examinations made by the older methods. 



The milk of nine goats in the Station flock was also examined, 

 and gave astonishingly high cell counts, the average for these goats 

 and two others previously studied being nearly seven and a half 

 million cells per unit. As goat milk is used with great success in 

 the nutrition of infants and invalids, it would seem that high cell 

 counts can not be a reliable indication of poor sanitary quality. 



The average obtained for the Station herd repre- 



Variations and sents wide variations, not only in different cows but 



fluctuations also in the same cow at different times and in 



in cell counts, separate quarters of the same udder at the same 



time. The greatest average number of cells occurs 



incolostral milk; but equally large numbers of cells are occasionally 



found in milk drawn at any time during the lactation period. Several 



very high cell counts have been obtained from the milk of cows near- 



ing the end of lactation, and such high counts appear to be more 



common at this time than near the middle of the time in milk. 



The average counts for the latter half of the period, however, are 



not markedly higher than those for the earlier half. As the quantity 



of milk is less toward the end of lactation the whole number of cells 



discharged is lower than during the earlier part of the period. 



Marked variations occur in the numbers of cells found in the 

 milk from day to day; but the cause or causes of these fluctuations 

 have not yet been discovered. There is uniformly a larger number 

 of cells in the strippings than in milk previously drawn, but it was 

 not possible to assign a cause for the increase in cell counts in the 

 strippings. No constant relationship could be found between the 

 counts for the first streams from the udder and those from samples 

 taken later. 



