52 



ESSENTIALS OF BACTERIOLOGY. 



ture of 65 to 68 C., until coagulation occurs ; then removed 

 and sterilized. 



Fio. 22. 



Babe's incubator. 



Thermo-regulators. 



Sterilization of Blood Serum. The tubes are placed 3 to 4 

 days in incubation at 58 C., and those tubes which show any 

 evidences of organic growth are discarded. 



If now, at the end of a week, the serum remains sterile at the 

 ordinary temperature of the room, it can be used for experi- 

 mental purposes. 



Perfectly prepared blood serum is transparent, of a gelatine- 

 like consistence, and straw-color. It will not liquefy by heat, 

 though bacteria can digest it. Water of condensation always 

 forms, which prevents the drying of the serum. 



J31ood serum, formerly much more used than now, was especi- 



