Cooperative Work with Columbia University 405 



purifying it. What is considered by most people to be good wash- 

 ing does not make such strainers sutiiciently clean to pass milk 

 through them. The metal strainers, or the cotton strainer made 

 especially for the purpose and used only once, are better. Where 

 milk can be produced by clean methods, no strainer is necessary. 



KEEP MILK COLD 



The sooner milk can be cooled, the better. It is almost impos- 

 sible to produce milk without some bacteria in it, so that the 

 problem now is to prevent these bacteria from increasing in num- 

 ber. At a temperature of seventy degTees, one bacterium may 

 increase to two in twenty minutes; while at fifty degrees it 

 requires a very much longer period. One bacterium in milk at 

 fifty degrees may increase in twelve hours to six or seven, while 

 at seventy degrees it may increase to 600 or 700. When, there- 

 fore, it is remembered that much apparently good milk contains 

 many thousands of bacteria per cubic centimeter, which is about 

 thirty drops, it is readily seen how soon millions of bacteria will 

 develop when the milk is warm. Milk should be cooled as soon 

 as possible to fifty degrees or lower, and kept at that temperature. 

 The following table prepared by Professor Stocking shows the 

 importance of keeping milk cool. The milk used in this experi- 

 ment was clean and of high quality. 



Effect of Different Tempekatures Upon the Development of Bacteria 



IN Milk 

 Temperature Bacteria per c.c. 



maintained at end of 12 



for 12 hours hours 



40 degrees F 4. 000 



47 degrees F 9, 000 



50 degrees F 18, 000 



54.5 degrees F 38. 000 



60 degrees F 453, 000 



70 degrees F 8, 800, 000 



80 degrees F 55, 300. 000 



COOLERS 



Various styles of apparatus are on the market for cooling milk. 

 The open type that is so common should be kept in a clean room, 

 free from dust, to prevent the contamination of milk during cool- 

 ing. In a dusty room, millions of bacteria may be added to milk 



