100 BACTERIA IN MILK 



The results of Harrison ^^ are equally interesting. The 

 organisms falling on an area equal to a circle having a diameter 

 of 12 inches were found to vary from 12,210 to 42,750 during 

 bedding, feeding and cleaning up, whilst one hour later similar 

 tests gave only 483 to 2370 organisms. 



Orr 1^ by exposing plates of nutrient medium for five min- 

 utes and afterwards incubating for four days at 20° C. obtained 

 from 1260 to 4500 organisms per 113 square inches (area of 

 circle 12 inches in diameter). The author has found that in 

 clean, well-ventilated cow byres as low a germ content as 200 

 per 113 square inches could be attained when tested with plates 

 of nutrient agar for five minutes and incubated at 37° C. for 

 forty-eight hours. Coliform bacilli, as shown by neutral red 

 lactose agar plates, were usually absent. 



The influence of milk containers is also well marked. Back- 

 haus found that fresh milk which originally contained only 6600 

 bacteria per c.cm. was increased in germ content to 97,000 per 

 c.cm. by passage through six containers. Wooden pails were 

 the most objectionable in this respect as they averaged 280,000 

 germs as against 1690 for galvanized iron and 1105 for enam- 

 elled ware. Pails after rinsing contained 28,600 organisms and 

 sterilized pails only 1300. Harrison ^* also investigated the 

 cleansing of cans; by rinsing the vessels with 100 c.cms. of 

 sterile water he obtained the following results: 



Bacteria per c.cm. 



Improperly cleaned cans 215,000-806,320 



Washed with tepid water and scalding 13,080- 93,400 



Washed with tepid water and steaming 5 mins. . . 355- 1,792 



Cloth and absorbent cotton strainers may also be a source 

 of bacterial contamination unless proper precautions are taken. 



Milk coolers of the open type may introduce contamination 

 from both the cooler itself and from the air. This is well exem- 

 plified by the results both of Orr ^^ and the author. (Table XL.) 



Two other sources of milk contamination are water and cow 

 faeces. It is obvious that all the water used for cleansing and 



