New York Agricultural Experiment Station. 163 



arranged in Table XIII according to the month of lactation. This 

 gives a total of 246 tests made on 126 different cows of different 

 breeds and from widely different regions. All of these cell counts 

 except those in Column la and a few in Columns XI and XII were 

 made from milk sufficiently normal in appearance to have been 

 used. Three or more of the cows tested had had udder troubles 

 at some time or other and as many as six possibly tubercular animals 

 are included. 



It is seen at once from the averages that even this number of 

 tests is insufficient to show what the real conditions are. The dif- 

 ferences between the numbers averaged are so great that a few 

 large counts very materially affect the averages. It seems clear 

 that the cell counts of the first three days of lactation average much 

 higher than those of later periods although equally high cell counts 

 are seen in almost all of the later periods. When the counts are 

 separated into two groups at the 500,000 per cubic centimeter mark, 

 it is found that the ratio between the number of counts under this 

 mark to the number of counts over this mark during the first six 

 months of lactation (exclusive of counts obtained from colostral 

 milk) is 100:52. The similar ratio for the counts obtained during 

 the second six months is 100:82. That is, the majority of the high 

 cell counts here given occurred during the latter part of the lacta- 

 tion period. 



The lowest average cell counts given in Table XIII occur during 

 the months when the greatest amount of milk is secreted (third to 

 seventh month). Inasmuch as the cell counts are all given on the 

 cubic centimeter basis and inasmuch as the numbers of cells found 

 during the latter portion of the lactation period when the total 

 amount of milk secreted is small are not decidedly different from 

 those found during the earlier portion, it is evident that the total 

 number of cells discharged from the udder at a single milking averages 

 less during the latter portion of the lactation period. 



III. EFFECT OF THE VACUUM COW MILKER ON THE 



CELL COUNT. 



Because of the fact that vacuum milking machines have frequently 

 been accused of causing so-called " leucocytosis " and also because 

 the question is frequently asked whether high vacuums do not suck 

 blood out of the interior of the udder, three series of observations were 



