270 CLEAN MILK 



After heating for about 15 minutes, filter through cotton, tube and 

 autoclave at 15 lbs. for 15 minutes. 



(This substitute was suggested by H. W. Hill in 1898, worked 

 out by A. J. Chesley, and adopted in the Minnesota State Board of 

 Health Laboratories, 1908.) 



Potato Medium. — Good sized, plump potatoes, free from bad 

 spots, are well washed and peeled ; cylinders of a size to fit the test 

 tube are cut from them with a cork borer of appropriate size to 

 slip into the test tubes; the cylinders are cut diagonally across and 

 the resulting half-cylinders washed over night in running water; 

 they are then dropped, large end down, one half-cylinder to a tube, 

 into test tubes containing wads of cotton, saturated with water^ 

 pushed to the bottom of the tube, the potato resting on the wet 

 cotton; the tubes are then plugged and sterilized. Note: Potato 

 remaining sharply acid to litmus paper after the over-night wash- 

 ing, should be rejected. 



Nitrate Broth. — Dissolve 1 gram peptone in one litre of water ; 

 add 2 grams nitrite-free potassium nitrate; adjust to 1% (normal), 

 acid to phenolphthalein, tube and sterilize. 



Lojjler's Blood Serum. — To glycerine dextrose broth 3 parts, 

 add 1 part fresh serum (obtained by collecting cow, pig, horse, etc., 

 blood in a clean pail and allowing it to stand , in cold storage for 

 24 hours ; the blood clots, the clot shrinks, and with care, the straw- 

 colored serum or liquid part may be drawn off with a syphon or 

 large pipette). Adjust reaction to 0.8% acid, and coagulate thus: 

 slope tubes to get a large surface, being careful not to wet plugs, 

 in an autoclave, which does not leak steam at all. Run up sloivly 

 to ioo° C, taking great care that all the air is driven out by the 

 steam. After maintaining the temperature at ioo° C. for 20 

 minutes, close outlet cock and run up slowly to 15 lbs. pressure, 

 still preventing even momentary escape of steam even from one 

 safety valve. Hold at 15 lbs. for 15 minutes, then cut off steam 

 or gas supply and cool to room temperature before opening. Open. 



