28 GENERAL CONDITIONS AFFECTING BACTERIA IN MILK 



philes of human blood, and are present in small numbers in healthy 

 milk. In the early stage of lactation, however, they are present in 

 considerable number, and may occur so generally as to constitute 

 leucocytosis. 



A third cell not infrequently present in milk is the/«i" cell pure 

 and simple. It is always present in the milk of cows suffering from 

 infectious mammitis. Stokes and Wegefarth carried out a series of 

 experiments to show the percentage of milk which under various 

 conditions contains pus cells. They examined the milks of three 

 grades or groups of cows as follows : — 



{a) lOO cows in the country, kept in a well-ventilated stable with 

 roomy stalls and upon good pasturage. They were fed while in stall 

 on bran, ground corn, and hay. They were groomed and cleaned 

 daily, and inspected by competent veterinary inspectors. All sick 

 animals were isolated from the herd, and the milking operations 

 were carried out in a cleanly manner. 



On microscopical examination of the milk of this group it was 

 found that it gave a general average of i-i pus cell to the field of 

 the microscope.^ There were practically no pus organisms, such as 

 streptococci or staphylococci ; 75 cows gave an average of less than 

 I pus cell to the field ; 93 cows out of 100 gave less than 5 cells ; 

 whilst 98 cows out of 100 gave less than 10 pus cells; and 

 45 cows gave a percentage of o-i pus cell to the field. In each 

 case fair samples and fields were chosen. 



{b) The second group consisted of 50 cows in the country, 

 stalled in badly ventilated narrow stalls, and running upon bad 

 pasturage. They were fed on distillery grains, cut hay, and bran. 

 The sanitary precautions carried out in the first group were not 

 adopted. 



On microscopical examination of the milk this group gave an 

 average of 1 1-3 pus cells in the field of the microscope, as compared 

 with I- 1 in the first group. 



{c) The third group consisted of 100 cows kept in the city 

 always confined to stables, with narrow stalls, no ventilation, little 

 or no light, and no fresh pasturage. They were fed on brewery 

 grains, distillery slops, bran, and hay. The cows remained in the 

 stables for months together until dry. The milk was collected in 

 such a way as to obtain a fair average from the whole herd, and was 

 drawn under veterinary supervision. 



On microscopical examination, the milk of this group gave a 



* These averages are all based upon counts of ten microscopic fields, with ^ 

 oil immersion lens. 



