242 MILK HYGIENE 



as possible by agitation for five minutes, then burn 

 through the paste-board stopper with a hot iron and 

 remove the desired amount of milk with a sterile pipette. 



The interval between collection and analysis. Generally 

 speaking the shorter the time between the collection and 

 examination of milk samples the more accurate will be 

 the results. For routine work the attempt should be 

 made to plate within four hours of the time of collection. 



Too much stress cannot be laid on keeping the sam- 

 ples properly iced during this interval. They should be 

 kept below 40 F., but care should be taken that they 

 are not frozen. 



Dilutions. Ordinary potable water, sterilized, may 

 be used for dilutions. Occasionally spore forms are 

 found in such water which resist ordinary autoclave 

 sterilization ; in such cases distilled water may be used 

 or the autoclave pressure increased. With dilution 

 water in eight-ounce bottles calibrated for ninety-nine 

 cubic centimeters and in test tubes calibrated for nine 

 cubic centimeters all the necessary dilutions can be 

 made. 



Short, wide-mouthed "Blakes" or wide-mouthed 

 French square bottles are more easily handled and more 

 economical of space than other forms of bottles or flasks. 



Eight-ounce bottles are the best, as the required 

 amount of dilution water only about half fills them, leav- 

 ing room for shaking. Long-fiber, non-absorbent cotton 

 should be used for plugs. It is well to use care in 

 selecting cotton for this purpose to avoid short-fiber or 

 " dusty" cotton, which gives a cloud of lint-like particles 

 on shaking. Bottles and tubes should be filled a little 

 over the 99 c.c. and 9 c.c. marks to allow for loss during 

 sterilization. 



The dilutions recommended are 1-10, 1-100, 1-1,000, 

 1-10,000, 1-100,000 and 1-1,000,000. 



For certified milk the 1-10 and 1-100 dilutions should 

 be used, while the 1-10,000 will usually be found best for 

 market milk. 



The 1-10 dilution is prepared by shaking the milk 

 sample twenty-five times and then transferring 1 c.c. 

 of the milk to a test tube containing 9 c.c. of sterile 

 water. 



