75 



is thoroughly disinfected and turned back, the artery ex- 

 posed, a sterile glass canula inserted and the blood collected, 

 by means of a sterile rubber tube attached to the canula, in 

 a sterile flask. After the serum is formed it can be drawn 

 o£E with a sterile pipett j, and distributed in small sterile test- 

 tubes (5 — 7 c.c. in each). It is well to set the liquid serum 

 in an incubator for a few days to test its sterility. The tubes 

 of liquid serum are inclined (the same as agar) and placed 

 in a blood serum sterilizer, or other chamber in which the 

 temperature can be raised to 70° or 75" C, and kept there 

 until the serum has set. Isabel and store. 



If larger quantities of the blood are required, it is more 

 convenient to collect it from the bleeding animals (cattle or 

 sheep) in a slaughter house. It is often necessary to sterilize 

 the liquid serum after it has been distributed in tubes (5 c.c. 

 in each), when it has been collected in this manner. This 

 can be done by heating them in a water bath at 62° C. for 

 2 hours each day for four consecutive days. 



§ 129. The preparation of Loeffler's blood serum. 

 This consists of neutral bouillon (prepared from meat) con- 

 taining I % glucose, I part, liquid blood serum 3 parts. 

 Mix and distribute in sterile test tubes, incline and solidify 

 the same as blood .serum. The temperature should be about 

 7.5" C. and the exposure will be necessarily longer than for 

 the pure blood serum. Label and store. 



For other methods of preparing serum and other special 

 media. See text-books. 



§ 130. Staining bacteria by Gram's method. Prepare 

 the cover-glass preparations as already described. Stain 

 them in gentian-violet aniline water or in a saturated alco- 

 holic .solution of gentian violet in 5% carbolic acid in the 

 proportion of i to 20 for from 5 to 7 minutes. Rinse in 

 water and transfer them to a watch glass containing Gram's 

 solution until the color becomes quite black. This requires 

 from one to two minutes ; then place the preparations in a 



