54: Retort or the Department of Bacteriology oy the 



was chosen as the best available unit with an appreciation of its 

 deficiencies. It is expected that the quantitative studies of the 

 germ content of the barn air which are now being pursued will furnish 

 a more scientific unit for such comparisons and the results obtained 

 by the newer method will furnish a means for checking the accuracy 

 of the results here presented. It is believed that by using the same 

 cows and the same milkers throughout each experimental study the 

 objections to the unit of exposure were met with fair success. 



Pail used. — The material falling from the body of the cow during 

 the milking process furnishes a considerable part of the germs which 

 enter the milk through the air. The study of modern milk pails 5 has 

 shown that by their use the larger part of this contamination may be 

 prevented, and since they have many good features with practically 

 no unsatisfactory ones they are rapidly becoming a part of better 

 dairy practice. Therefore, with the exception of the studies of 

 methods of sampling which were made in connection with the milking 

 machine, an improved Loy pail such as was fully described in Bulletin 

 No. 326 was always used in these studies. 



Cleaning of pails. — The pails were cleaned with hot water, sal- 

 soda and a brush in the ordinary way, followed by an exposure to 

 flowing steam in a steam box for 15 minutes. 



Protection of the pails. — After being steamed the pails pemained in 

 the steam box until milking time when they were taken to the barn 

 by one of the authors and delivered to the milker when he was pre- 

 pared to begin the actual milking process. As a further protection 

 the top of each pail was covered with a cloth before it was placed in 

 the steam box and this cloth remained upon the pail until it was 

 handed to the milker. The influence of this protection upon the 

 germ content of the milk is discussed on page 61. 



Sampling. — Since the importance of these barn operations is to be 

 judged by the number of germs found in the samples of milk it is of 

 the greatest importance that these samples shall accurately represent 

 the true germ content of the pail of milk. The details of a study of 

 this question of methods of sampling are given on page 55. As a 

 result of this study the method adopted was to remove the pail of 

 milk immediately to an adjoining milk room, stir it thoroughly with 

 a sterile long-handled spoon and with the spoon transfer a sample to a 

 sterile test tube. 



b See footnote 3, p. 198. 



