UNITED STATES DEPARTMENT OF AGRICULTURE 

 BULLETIN No. 642 



Contribution from the Bureau of Animal Industry 

 JOHN R. MOHLER, Chief 



Washington, D. C. 



April 30, 1918 



THE FOUR ESSENTIAL FACTORS IN 



THE PRODUCTION OF MILK OF LOW 



BACTERIAL CONTENT 



By 



S. HENRY AYERS, LEE B. COOK, and PAUL W. CLEMMER 

 of the Dairy Division 



CONTENTS 



Factors Influencing the Sanitary Quality of Milk 1 



Objects of the Investigation 3 



Description of Barn and Methods Used in the Production of the Milk . . 3 



Method of Sampling and Making the 3acteria! Count 5 



The Experimental Work 5 



Contamination of Milk by Unsteriiized Utensils . « . . 25 



Contamination of Milk by Manure and Dirt 32 



The Three Most Essentia! Factors in the Production of Milk of Low Bacte- 

 rial Content 38 



A Practical Demonstration on Six Farms 39 



Bacterial Counts of Fresh Milk on the Average Farm 43" 



The Effect of Temperature on the Growth of Bacteria in Milk ...... 45 



Summary 58 



Conclusions 59 



Literature Cited 61 



WASHINGTON 

 GOVERNMENT PRINTING OFFICE 



1918 



