SOLID TRANSPARENT MEDIA. 



57 



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. 



FIG. 26. 



Thermostat for blood serum. 



Preservation of Blood Serum in Liquid State. Kirchner advises 

 the use of chloroform. To a quantity of serum in a well-stop- 

 pered 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. 



