SOLID TRANSPARENT MEDIA 59 



may be prepared in a shorter way by coagulating the serum at 

 a temperature short of boiling-point. Sterilization is completed 

 in three days by exposing 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 



Fig. 26. Incubator. Fig. 27. Thermoregulators. 



well-stoppered flask a small amount of chloroform is added 

 enough to form about a 2 mm. layer on the bottom. 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 chloroform 

 has been driven off (determined by absence of characteristic 

 odor); the serum is then solidified and sterilized as in the 

 ordinary way. 



