36 BULLETIN" 642, U. S. DEPAETMENT OF AGRICULTURE. 



ations in the quantity of sediment as well as in the bacterial count, 

 but on the whole there was a strikingly close relation. Plate V shows 

 that after the morning milking on October 22 there was a decided 

 drop in the quantity of sediment as well as in the bacterial count. 

 On that date the manure was removed from the stable in the after- 

 noon. That night's milk showed decidedly less sediment and a lower 

 bacterial count, as did also both milkings of October 23. The results 

 show that there is some direct relation between the sediment and 

 bacterial count which always may be influenced by the variable num- 

 ber of bacteria in the manure. It is therefore quite evident that the 

 sediment test is of value only under certain conditions. 



Bacterial counts shown in Plate V are particularly interesting 

 since they show that a very large quantity of sediment, in other 

 words, manure, is necessary to create high counts provided the princi- 

 pal source of contamination is manure. In the experiment in which 

 the manure was not removed nor the cows cleaned for nine days, the 

 highest count obtained was 1,550,000, and the next highest was 

 1,150,000 bacteria per cubic centimeter. The other counts ranged 

 from 6,600 to 150,000 bacteria per cubic centimeter. After the 

 manure was removed the experiment was repeated under similar con- 

 ditions for 10 days. During the latter period the highest count ob- 

 tained was 82,000 and the lowest 6,600. In both experiments steril- 

 ized utensils were used; consequently, the contamination was due 

 principally to the introduction of manure into the milk. The figures 

 indicate that counts above 200,000 per cubic centimeter in milk usu- 

 ally should not be attributed entirely to contamination from manure. 



The number of bacteria in 57 samples of fresh cow manure was 

 determined, and the results are shown in Table 16. The range in 

 number of bacteria per gram was from 2,900,000 to 690,000,000, the 

 average number per gram being 49,615,611. From these results it can 

 be assumed, therefore, that the average bacterial content of fresh 

 manure is about 50,000,000 per gram. From that number it is possi- 

 ble to calculate the number of bacteria added to each cubic centimeter 

 of a pint of milk through contamination bj r definite quantities of 

 manure. Table 17 shows the number of bacteria that would be added 

 to each cubic centimeter of milk if fresh manure were added in quan- 

 tities varying from 0.5 to 0.01 of a gram, assuming an average gram 

 sample to contain 50,000,000 bacteria. The figures show that 0.5 

 gram of fresh manure would add 52,851 bacteria to each cubic centi- 

 meter of a pint of milk, while 0.01 of a gram of manure would add 

 1,057. 



