Xew York Agricultural Experiment Station. 53 



pails with cloth " and " Observations on methods of sampling," the 

 figures covering the effect of plastering and painting the stable but 

 not the test of the effect of whitewashing, and the preliminary experi- 

 ment on the effect of clipping cows. During the remainder of the 

 investigations this work was done by Mr. Ruehle. The responsibility 

 for controlling the barn conditions during the progress of the experi- 

 ments has rested upon Mr. Smith, who has personally supervised 

 the barn and dairy operations in connection with the experimental 

 milkings. Those most familiar with the difficulties attending this 

 class of experimental work will undoubtedly be surprised at the 

 accordant results extending over so many years. The secret of this 

 uniformity in results lies largely in the success with which barn con- 

 ditions were held to a definite standard during the. experiments. The 

 wide variations which so commonly occur in experiments of this 

 nature are probably due quite as much to lack of control of important 

 factors affecting the thing being measured as to errors in measure- 

 ment. Mr. Harding assisted in planning and supervising the experi- 

 mental work and in preparing the results for publication. 



TECHNIQUE. 



With the exception of the germs from within the udder and those 

 introduced by the utensils and the hands of the milker all germs 

 enter the milk through the air. The number which enter depends 

 upon the germ content of the air and the length of time during which 

 the milk is exposed to it. The actual exposure varies greatly under 

 different conditions of barn management but with hand milking the 

 time of exposure during the milking process is fairly definite, ranging 

 between five and ten minutes. Ordinarily the longer milking periods 

 are associated with larger yields of milk so that when the results of 

 the exposure are expressed in germs per cubic centimeter these num- 

 bers are fairly comparable. 



Unit of exposure. — Under no system of hand milking is it possible 

 to reduce the exposure of the milk below that taking place during the 

 milking process. Accordingly in these studies the exposure em- 

 ployed in measuring the influence of a given barn operation upon the 

 germ content of the milk was that occurring during the actual milking 

 of the cows. 



It may be objected that the variation in time required to milk 

 different cows renders this unit too variable to be satisfactory. It 



