CULTURE MEDIA 93 



sides of the jar with a glass rod. It may be left on the ice for 

 from twenty-four to forty-eight hours. At the end of that time 

 the serum will have separated from the clot and may be drawn 

 off with a siphon into tubes. These tubes are sterilized for the 

 first time in a slanting position, as the first sterilization coagulates 

 the serum. The coagulation may be done advantageously, as 

 advised by Councilman and Mallory, in the hot-air sterilizer at a 

 temperature below the boiling-point. After coagulation, sterilize 

 in the autoclave at 110 C. for 20 minutes. This serum makes an 

 opaque medium of a cream color. Blood-serum may be more 





FIG. 35. Koch's serum sterilizer. 



conveniently sterilized in the Koch serum inspissator (Fig. 35). 

 A clear blood-serum is to be obtained by sterilization at a tempera- 

 ture of 58 C. for one hour, on each of six days, if a fluid medium 

 is desired, or of 75 C. on each of four days if the serum is to be 

 solidified. In the latter case the tubes are to be placed in an in- 

 clined position. Opaque, coagulated blood-serum has most of 

 the advantages of the clear medium. Blood-serum may be se- 

 cured from small animals by collecting blood directly from the 

 vessels, and with proper technic may be obtained in a sterile 

 condition; and the serum may be separated and stored in a fluid 

 state. Human blood-serum is sometimes obtained from the 



