PRODUCTION OF MILK OF LOW BACTERIAL CONTENT. 



31 



As a matter of additional interest, some experiments were con- 

 ducted which show that bacteria grow in washed cans which are 

 closed before they are thoroughly dried. To illustrate the point, two 

 5-gallon cans were sterilized, then one was filled with milk, which 

 was immediately poured into the other, and that in turn immediately 

 emptied. The operation was performed in order to introduce into 

 each can approximately the same number of bacteria. Each can 

 was then washed in exactly the same manner, the excess of water 

 being shaken out and the cover replaced. A determination of the 

 number of bacteria in one of the freshly washed cans was then made. 

 The other can, which it may be assumed contained approximately the 

 same number of bacteria at that time, was allowed to stand at a 

 warm temperature for 24 hours, when the number of bacteria was 

 determined. An examination of the results in Table 13 shows that 

 in each of the seven tests there was a great increase in the number 

 of bacteria in the cans during the holding period of 24 hours. The 

 importance of drying cans thoroughly after washing, particularly 

 when they are immediately covered, is therefore evident. 



Table 13. — Bacterial groicth in cans covered before being dried. 





Bacteria per can. 



Series No. 



Bacteria per can 



Series No. 



Freshly 

 washed. 



24 hours after 

 washing. 



Freshly 

 washed. 



24 hours after 

 washing. 



1 



960, 000 

 618, 000 

 137, 000 

 91, 000 



847,000.000 



2, 612, 000, 000 



336, 000. 000 



428, 000, 000 



5 



99. eoo 



5, 570. 000 

 305, 000 



320, 000. 000 



2 



3. 



4 



6 



7 : 



748, 000. 000 

 138, 000, 000 



Utensils that have not been sterilized, besides adding large num- 

 bers of bacteria to milk, introduce types which greatly affect the re- 

 lation of the various bacterial groups in it. This matter also was in- 

 vestigated, determinations having been made of the bacterial groups 

 in milk drawn directly from the udder, from sterilized utensils, from 

 unsterilized utensils, and from washings of unsterilized cans. Table 

 14 summarizes the results of this work. Numerous samples from 

 different sources have been averaged in the table. The bacterial 

 groups were determined by the milk-tube method, which has been 

 described. 



The bacterial groups in the samples of milk drawn directly from 

 the udder compare very closely with those in the milk from sterilized 

 utensils. It will be noted that in the milk from unsterilized utensils 

 there was a great increase in the percentage of the alkali-forming 

 and peptonizing groups. While the acid-coagulating peptonizing 

 group was not found in milk from utensils not sterilized, it was pres- 



