38 BULLETIN" 642, U. S. DEPARTMENT OF AGEICULTTJEE. 



THE THREE MOST ESSENTIAL FACTORS IN THE PRODUCTION 

 OF MILK OF LOW BACTERIAL CONTENT. 



< In connection with the term " production of milk " as used in this 

 paper, it is evident that there are three essential factors which most 

 influence the bacterial content. Named in the order of their im- 

 portance they are, first, the use of sterilized utensils; second, clean 

 cows, particularly the udders and teats ; third, the use of the small- 

 top pail. By the use of these factors it has been possible to produce 

 milk of a low bacterial count and practically free from visible dirt 

 in an experimental barn which represents a poor type found in this 

 country. In fact, the counts obtained were so low that only 2,000 /to 

 3,000 bacteria per cubic centimeter were introduced through external 

 contamination. A large number of factors not considered in this 

 paper are responsible for this contamination. Some of them have 

 been extensively studied by Stocking (1), Harding (9), Euehle (10), 

 and Prucha (11). 



It is evident, therefore, that the three simple factors mentioned 

 prevent most of the contamination of milk. It is possible, however, 

 that under some circumstances low-count milk can not be produced 

 by means of these few factors. It has been shown that they prevent 

 most of the external contamination and that by their use it is possible 

 to produce milk with a bacterial content very nearly as low as that 

 drawn directly from the udder. If milk drawn directly from the 

 udder is high in bacteria, it is impossible under any conditions to 

 produce a low -count milk. 



It is well known that freshly drawn milk from some cows is some- 

 times high in bacteria ; if there are, therefore, a number of such cows 

 in a herd, the bacterial content of the mixed milk will be relatively 

 high. As an example it may be well to mention a case in which milk 

 produced in a sanitary barn from clean cows and with sterilized 

 utensils averaged 5,096 bacteria per cubic centimeter for 28 samples. 

 In the herd there were cows whose milk occasionally was abnormal, 

 in that it contained a few small clots and the last milk sometimes was 

 slightly stringy. The milk from these cows was kept separate from 

 the regular herd milk, with the result that 28 samples of it, produced 

 at the same time as the other samples, averaged 137,786 bacteria 

 per cubic centimeter. It is therefore evident that with cows of that 

 type it would be impossible under any conditions to produce a low- 

 count milk. 



It is not known how common such cows are in this country, and 

 the point is mentioned merely to show why it is sometimes impossible, 

 even with the three essential factors, to produce milk of low bac- 

 terial count. 



The criticism may be raised that the value of the essential factors 

 was determined under experimental conditions which do not repre- 



