UNITED STATES DEPARTMENT OF AGRICULTURE 
BULLETIN No. 642 
Contribution from the Bureau of Animal Industry 
JOHN R. MOHLER, Chief 
Washington, D. C. v April 30, 1918 
THE FOUR ESSENTIAL FACTORS IN 
THE PRODUCTION OF MILK OF LOW 
BACTERIAL CONTENT 
5 By 
.S. HENRY AYERS, LEE B. COOK, and PAUL W. CLEMMER 
of the Dairy Division 
CONTENTS 
Factors Influencing the Saniiary Quality of Milk 
Objects of the Investigation 
Description of Barn and Methods Used in the Production of the Milk 
Method of Sampling and Making the Bacterial Count 
The Experimental Work 
Contamination of Miik by Unsterilized Utensils 
Contamination of Milk by Manure and Dirt 
The Three Most Essential Factors in the Production of Milk of Low Bacte- 
rial Content : 
A Practical Demonsiration on Six Farms 
Bacterial Counts of Fresh Milk on the Average Farm 
The Effect cf Temperature on the Growth of Bacteria in Milk 
Summary 
Conclusions 
WASHINGTON 
GOVERNMENT PRINTING OFFICE 
1918 
