32 



BACTERIOLOGY FOR NURSES 



through the filter a second time. Media which solidify when 

 cool should be filtered in a warm place. 



Tubing of Media. For the most part media are used in test 

 tubes. An improvised apparatus (Fig. 9) may be arranged for 

 filling them as follows : A piece of rubber tubing is attached at 

 ( one end to a glass funnel and at the other to a glass point; a 

 pinchcock is fixed at the center of the tube. The plug is removed 

 from the tube by taking it between the third and fourth fingers 



of the right hand and the glass 

 point is placed almost to the bot- 

 tom of the test tube in order to 

 prevent the medium touching the 

 neck of the tube where the cotton 

 plug might stick. About 7 c.c. 

 of medium is sufficient for each 

 tube. The next step is steriliza- 

 tion by the method most suitable, 

 after which the medium is ready 

 for use. 



Preparation of Culture Media 

 in Common Use. The basis of 

 the most commonly used media 

 is an infusion of meat, or meat 



FIG. 9. Apparatus for tubing Media. t_ r 11 



extract, to which a small amount 

 of peptone and sodium chloride is added. 



Meat infusion is prepared as follows: One liter of water is 

 poured over one pound of finely chopped beef or veal. It is heated 

 at a temperature of 50 C. for one hour or it may be allowed to 

 remain twenty-four hours in the refrigerator and not heated. 

 The infusion is then strained through cheesecloth and all the juice 

 thoroughly pressed out of the meat. The fluid contains soluble 

 albumins, extractives, muscle sugar, and salts. 



As a substitute for meat infusion Liebig's extract 2 to 3 grams 

 per liter of water may be used. 



