BACTERIOLOGICAL TECHNIC. 



51 



necessary skill and experience to prepare culture media. He should explain 

 to a few representative physicians that he is ready to prepare such media as 

 the^ busy physician may require. The physicians wUl in all probabUity 

 indicate what media are likely to be needed in the course of their practice. 

 Allow yourself to be guided by these several suggestions and prepare the 

 media accordingly. 



Make sure that the culture media are clear. There must be no sediment 

 and no flocculency. Not infrequently the medium fails to become sufficiently 

 clear, even though every precaution has been taken. In such cases clari- 

 fication may be tried, rather than to discard it. Add the white of an egg, thor- 

 oughly beaten, to a liter of the medium in the liquid state and at a tempera- 

 ture below the coagulating point for albumen, mix 

 thoroughly; boil for ten minutes, and filter. The 

 coagulating albumen takes up the impurities which 

 remain upon the filter with the albumen, while the 

 medium comes through perfectly clear. Media which 

 have become infected with bacteria as the result of 

 inadequate setrilization should be discarded. Do not 

 attempt to clarify them. They may become clear, 

 but they are nevertheless objectionable because of the 

 substances which the bacteria may have liberated and 

 which might interfere with the development of the 

 bacteria to be grown in it subsequently. 



Most of the tubes with solid media (Loeffler's automatic devise sliuts 

 serum, gelatin, agar, and gelatine-agar) should be 

 slants. The slanting surface offers certain advantages in making diag- 

 nostic bacterial cultures. The usual, non-slanting tubes, for deep stab 

 cultures, should, however, also be held in readiness. Keep all tubes 

 in suitable containers, in a dry, cool, clean place. To guard against 

 infection by mould and other organisms, it is well to cap all tubes with the 

 rubber caps or the tin foil dipped in corrosive sublimate and paraffin, as 

 already suggested. In case of liquid media, the rubber stoppers or the 

 rubber caps are much preferred, or the hot paraffin may be painted over the 

 tin foil and upper end of tube by means of a small brush. Apply two or 

 three coats. Thus protected, there is no danger of outside infection. 



The chances are that the physician who calls for tube culture media will 

 also require the use of an incubator. This the pharmacist should have in 

 readiness. The usual copper double-walled water-jacket incubator, with 

 thermo-regulator, kept at a temperature of about 25° C, will serve the 

 purpose. 



The swab to be supplied with each tube of slanted Loeffler's serum 

 consists of a piece of wire or of pine wood four inches long, around the 



Fig 25. — Koch safety 

 burner. Should the 

 flame be blown out, an 



