122 MICROBIOLOGY 



two of melted agar is run along each side of the block to fill 

 any angles between it and the cover-glass. After drying in 

 the incubator for five minutes it is placed over a hollow slide 

 and sealed with paraffin." 



Film or cover-glass preparations. These are made from 

 cultures of different kinds and also from other material con- 

 taining bacteria, such as animal tissues, milk and the like. 

 The following procedure may be recommended for making 

 cover-glass preparations: (a) From bouillon cultures. Place 

 two clean cover-glasses on the tray. With the loop remove a 

 drop of the bouillon culture and spread it in a thin layer 

 over about two-thirds of the surface of the cover-glasses. 

 One loopful will ordinarily make from 2 to 4 preparations. 

 Allow the liquid to dry on the cover-glasses in the air and, 

 when dry, fix the bacteria to them by passing them, film up- 

 ward, three times through the middle of the upper half of the 

 gas flame. Each passage (complete circle) should not occupy 

 more than one second. After fixing they are ready for stain- 

 ing. (&) From cultures on solid media. Place the cover- 

 glasses on a tray, and on the center of each put a drop of 

 sterile water or bouillon. Touch the surface growth of the 

 culture with the end of the needle and then gently rinse it in 

 the liquid on the covers. Spread the liquid on the covers as 

 before. From this point the procedure is the same as that 

 for preparations made from a bouillon culture, (c) From 

 tissues. With a pair of fine forceps take up a bit of tissue 

 from the freshly cut liver, spleen, or kidney, and rub it 

 gently over the surface of a clean cover-glass, care being 

 taken that the film or tissue is thin. Allow this to dry in the 

 air, after which pass the cover-glass, film up, three times 

 through the flame to fix the tissue to the glass. It can be 

 stained the same as the cover-glass preparations from the cul- 

 tures. When carbol fuchsin is used for staining, the prepara- 

 tion should be wet before applying the stain. These are often 

 spoken of as smear preparations. 



In making these preparations from blood, hold a cover- 

 glass by the edge and with the platinum loop place a drop of 



