New York Agricultural Experiment Station. 901 



Some of the cells found in milk are leucocytes — the white blood 

 corpuscles that are the active agents in destroying certain disease 

 germs in the body; and after the first week or so of lactation, the 

 presence of these leucocytes in the udder has been considered evidence 

 that they were attracted there because disease germs were in the 

 milk. It has been held, in particular, that there is a close relation- 

 ship between the presence of large numbers of cells and of the germs 

 that cause mastitis, or inflammation of the udder, a disease that 

 results in " gargety " milk. 



Boards of health in some large cities, and one National organiza- 

 tion, have adopted, as a standard for normal milk, a cell content 

 not exceeding 500,000 per unit (a cubic centimeter, or 18 to 20 

 drops); and would reject milk showing more cells than this as 

 abnormal and unfit for human food. 



It is therefore important that the dairy farmer should know what 

 justification there is for the belief that cells in milk are detrimental 

 in themselves or as indicators of abnormal conditions or disease in 

 the udder that might make milk unwholesome. 



The studies on the cell content of the milk of the 

 Studies at Station herd were made by Dr. Breed before he 



the Station, became a member of the staff; but his appointment 

 as Bacteriologist renders doubly appropriate the 

 publication, in a Station bulletin, of the valuable data secured. 



The three main purposes in this work and the extent of the in- 

 vestigations were as follows: 



(1) To make a number of examinations of the milk of individual 

 animals in order to determine the normal cell content of milk. For 

 this part of the work from five to eight samples were examined from 

 each of 21 cows in the Station herd, from 62 to 68 samples from each 

 of four other cows in this herd, and one sample from each of 53 

 cows in a Guernsey herd belonging to Mr. Alfred G. Lewis of Geneva. 

 In the summaries along this line data are also included relative to 

 the cell content of the milk of two other herds previously studied 

 by Dr. Breed and his associates, one at Meadville, Pa., of 41 cows, 

 and one in Germany of 3 cows. 



(2) To make detailed examinations of the milk of individual cows 

 in the hope that some reason could be discovered for the known 

 variations. These included studies on the effect on cell content of 

 period of lactation, age of cows, udder troubles, etc. For part of 

 this work two cows fresh in milk were used for one week and for 

 three weeks, respectively; four cows, more advanced in lactation, 

 for five weeks; and eighteen cows, near the end of lactation, for one 

 or two milkings. 



(3) To study the influence of the milking machine on the number 

 of cells discharged in milk. In these tests six cows were used for 

 about forty days in a detailed study of the effect of varying the 

 vacuum; two cows were under observation for 8 or 9 days in testing 



