Dirn^iox or aximal nrsuAyDRT 



395 



SESSIONAL PAPER No. 16 



(2) The Air a.s .\ Source op Cont.\mination of ^Filk. 



Tliis series of tests was carried on diiriiip: the month of April. The object, as 

 .'^tilted above, was to find approximately the reflation between the nnnibcr of bacteria 

 in the air of the barn and the nnmber in the milk. The weather, for the most part, 

 was snnny and dry. and, as would be expected, the counts were slightly higher than 

 i;i February and March. 



For the air test the method originally devised by Koch was followed. Agar plates 

 were exposed to the air during milking. The period of exposure was three minutes; 

 and the plates were placed upon a niilking-stool, which gave about the height of the 

 milk pail. They were exposed as near to the cow and the milker as possible, in order 

 to reproduce the conditions of milking. 



With each air test a corresponding test was made of the milk of the whole herd: 

 the sample was taken from the milk which had been cooled, strained, and bottled for 

 the consumer. Check tests were made in every case. Following are the results in 

 tabulated form: — 



(1) On this date liay was being chopped in the barn above and the air was full of dust. 



(2) The air plates were exposed after some of the heifers had been turned out. This 

 may account for the high air count, as compared with the milk count. 



From the figures it may be seen that the number of bacteria in the air of the barn 

 appears to correspond to a great extent with the number in the milk. Particularly 

 interesting is the test made on April 14, when an abnormal condition of the air 

 existed. Dust-laden air is followed by a correspondingly dirty sample of milk. 

 Excluding this abnormal case, the average of the counts shows: — 



Air plate — 75 colonies. 

 Milk plate — 19,550 colonies. 



Seven of the milk samples contained 20.000 or less per c.c. ; of these, six showed a 

 corresponding air count of less than 75. The remaining six show over 20.000 in the 

 milk: and all these have an air count of more than T"). Of the thirteen tests one 

 shows a marked variation (April 24). Considering the numerous other sources of 

 oontamination which might cause variations, the results are sufficiently uniform to 

 be convincing. The fact that air is a fertile source of milk contamination is, of 

 course, well established. The figures taken from tlicse tests are useful only in so 

 far as they magnify the danger of such contamination. 



Ag.\s.siz. 



