6 BULLETIN 642, U. S. DEPARTMENT OE AGRICULTURE. 



were obtained it was the intention, by the gradual elimination of 

 certain factors which contribute to the contamination of milk, to 

 produce milk that was practically free from visible dirt and had a 

 low bacterial content. Following that, the next step was to dupli- 

 cate the conditions in order to determine again the value of the 

 essential factors. To show clearly the scope of the work and the 

 conditions under which the milk was produced, the experiments are 

 listed in the order in which they were conducted : 



Experi- 

 ment No. Period covered. Conditions. 



1. July 22, to August 14, 1915 Cows and floor were dirty and the 



manure was removed weekly. The 

 utensils were not sterilized. 



2. September 14 to October 7. 1915 Cows and floor were dirty and the 



manure was removed weekly. The 

 utensils were sterilized. 



3. November 10 to 24. 1915 Cows and floor were dirty and the 



manure was removed twice a 

 week. Udders and teats of the 

 cows were washed and the utensils 

 were sterilized. 



4. February 27 to April 10, 1916 Cows "were clean and bedded, floor 



was clean, and the manure was 

 removed daily. Udders and teats 

 of the cows were washed ; also of 

 two others not washed. The uten- 

 sils were sterilized. 



5. April 11 to May 6. 1916 Cows and floor were dirty and the 



manure was removed weekly. The 

 utensils were sterilized. 



6. May 8 to 31. 1916 Cows and floor were dirty and the 



manure was removed weekly. The 

 utensils were not sterilized. 



7. June 5 to 13, 1916 Cows and floor were clean and the 



manure was removed daily. Ud- 

 ders and teats of the cows were 

 washed and the utensils were 

 sterilized. 



During the dates not covered by the periods above the cows were 

 kept in the barn and the relative value of the factors was studied by 

 other methods. The general conditions of the barn as previously 

 described.' method of feeding, etc., were not changed during the 

 experiments. The results obtained in the various experiments above 

 outlined will be described in their proper order. 



EXPERIMENT NO. 1 (COWS AND FLOOR DIRTY, MANURE REMOVED WEEKLY, 

 UTENSILS NOT STERILIZED). 



The first condition of the barn was one of extreme filth. Four cows 

 were placed there on January 28. 1915. and the first experiment was 

 begun on July 22 of that year. In the intervening period no atten- 



