92 MICROBIOLOGY 



coagulated. This takes about 30 minutes. It is important 

 not to boil the gelatin longer than is necessary for the coagu- 

 lation of the albumen. It is now ready for filtering which 

 must be done while the gelatin is hot. Filter through prop- 

 erly folded but ordinary paper, first moistened with boiling 

 water. Distribute the filtrate as desired. In pouring the 

 gelatin into the tube, use a small beaker or graduate, and see 

 that the gelatin does not touch the sides of the upper part 

 of the tube. Stand the tubes in a wire basket and sterilize in 

 a water bath or steam sterilizer. 



Blood-serum media. Blood serum may be sterilized by 

 fractional sterilization and remain fluid, or it may be ren- 

 dered solid by the application of a higher degree of heat in 

 sterilizing it. The blood is obtained from an ox, horse, sheep, 

 dog, or rabbit and collected in jars, flasks or tubes. When it 

 is to be used in a fluid state it should be drawn in an aseptic 

 manner into a flask from a vein by means of a sterile cannula 

 and rubber tube. When it is to be solidified, less care is 

 necessary. It is here sufficient to catch the blood from the 

 cut artery or vein in sterile jars or tubes. To facilitate clot- 

 ting it is well to have in the jar or tube something for the 

 clot to contract around. 



Preparation of Loeffler's blood serum. This consists of 

 1 part neutral bouillon (prepared from meat) containing 1% 

 grape sugar and 3 parts liquid blood serum. Mix and dis- 

 tribute in sterile test tubes, incline, and solidify the same as 

 blood serum. The temperature should be about 75 C., and 

 the exposure will be necessarily longer than for the pure 

 blood serum. When it is to be used for the cultivation of 

 diphtheria organisms it can be set at a much higher tempera- 

 ture (80 to 100 C.). Label and store. 



Blood serum for tubercle bacteria (Smith). 1 Dog's 

 serum is used. The dog is bled under chloroform and the 

 blood drawn from a femoral artery under aseptic conditions, 

 through sterile tubes directly into sterile flasks. The serum 



Smith. Jour. Exp. Med., Vol. Ill (1898) p. 451. 



