74 



ESSENTIALS OF BACTERIOLOGY 



way by coagulating the serum at a temperature short of boil- 

 ing-point. Sterilization is completed in three days by expos- 

 ing the tubes to a temperature of about 90 C. each day for 

 five minutes. Tubes so prepared are opaque and white. 



Preservation of Blood-serum in Liquid State. Kirchner 

 advises the use of chloroform. To a quantity of serum in a 



well-stoppered flask a small 

 amount of chloroform is 

 added enough to form about 

 a 2 mm. layer on the bot- 

 tom. If the chloroform is 

 not allowed to evaporate, 

 the serum remains sterile 

 for a long time. When 

 needed for use, test-tubes are 

 filled and placed in a water- 

 bath at 50 C. until all chlo- 

 roform has been driven off 

 (determined by absence of 

 characteristic odor); the se- 

 rum is then solidified and 

 sterilized as in the ordinary 

 way, or may be used hi a 

 fluid state. 



Human Blood-serum. 

 Blood-serum derived from 

 placenta, serum from ascitic 

 fluid and ovarian cysts, is 

 prepared in a similar manner 



Fig. 22. Incubator. 



to the above. 



Blood coagulum, suggested by the author, is the blood 

 itself (not the serum only) coagulated in test-tubes. It is 

 dark brown in color and allows some colonies of bacteria to 

 be more visible. It requires less time to prepare, and is not 

 so likely to become contaminated as when the serum is used. 



Loffler's Blood-serum Mixture. To 3 parts clear 

 serum add i per cent, glucose, beef infusion, and prepare as 

 above; tube. 



