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 PAut W. CLEMMER, Of the Dairy Division.' 
CONTENTS. 
Page. Page. 
Factors influencing the sanitary quality of The three most essential factors in the produc- 
AA cae egeeer perenne Meh Ao ee 1 tion of milk of low bacterial content....... 38 
Objects of the investigation.............-.--- A practical demonstration on six farms...... 39 
Description of barn and methods used in the Bacterial counts of fresh milk on the average 
production of the milk...-.-.........-..-.- PAIN Ay ae GN SY oN RIE eee Me ama 43 
Method of sampling and making the bacterial The effect of temperature on the growth of 
COUT eee epee es Giyaereich aiaton' SSC as 5 lORKCuS eke) hel OWN ee ooo dcosasuocbooSde 45 
mhevexpenimentaleworksse-ces- .-co-ere ss Drillapslbhoow ones he\ yas es ae ee ae eRme oat yee eet ae ay) 58 
Contamination of milk by unsterilized uten- Conclusions-sa25 a8 ese se cen eees ae ee 59 
Wie cbse dese Seen eee De sleiteratureicitedac. 26 see. cios saan ace eee ee 61 
Contamination of milk by manure and dirt... 32 
FACTORS INFLUENCING THE SANITARY QUALITY OF MILK. 
_ The production of milk of a high sanitary quality involves a 
knowledge of the influence of numerous factors. Whether these fac- 
tors are all grouped under one head and considered as a single unit 
or are grouped into several units, each directly connected with a 
separate phase of the production of sanitary milk, may not at first 
thought be of any importance. 
Consideration of that point, however, must lead to the view that 
to deal intelligently with the factors which influence the sanitary 
quality of milk they must be grouped in such way as to bring to- 
gether those which are of importance in connection with a definite 
phase of production. As an example, the question of abundant light 
1The authors acknowledge their indebtedness to T. E. Woodward, of the Dairy Division ; 
also to W. R. Hale and W. F. Turner, formerly of this division, who made the work 
possible through their supervision of the experimental barn. They also extend their 
thanks to the dairy farmers near Grove City, Pa., and to R. R. Welch, of this division, 
who assisted in making a practical demonstration of the work. 
18989°—18—Bull. 642 il 
