6 BULLETIN 642, U. S. DEPARTMENT OF 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. ; 
fee Suily. 22 10. Aueust. 145 191) 2g 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. 
=: November 10°t0. 24.101 2o2 = eee 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, fioor 
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. 
Se piiietel 40. May Oo OG es 3 ee Cows and floor were dirty and the 
manure was removed weekly. The 
utensils were sterilized. 
Ge Mayao tO 4, POLGl 2.2. = ea ee se Cows and ‘floor were dirty and the 
manure was removed weekly. The 
utensils were not sterilized. 
i SneRS LO. dos AOI Ge ot ee eee 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. 
Or 
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- 
