466 



BACTERIOLOGY. 



A temperature of 58°, maintained continuously for 6-8 

 hours, will cause the coagulation of blood-serum. Lofler's 

 serum and glycerin serum are not as readily affected. 



Fractional sterilization of serum at 75-80°. — At this tem- 

 perature ordinary blood- serum, and even Loffler's serum will 



coagulate. Conse- 

 quently, only solidified 

 serum will be obtained 

 by this procedure. The 

 method takes less time 

 than the preceding. It 

 yields an almost per- 

 fectly transparent yel- 

 low medium which is 

 a decided advantage 

 over the method to be 

 described next. The 

 cotton plugs of the 

 serum tubes should be 

 cut off close to the 

 end of the tube which 

 should then be turned 

 in a flame till the cot- 

 ton begins to change 

 The tubes are 

 with 



sterile, rubber caps. This precaution insures the steriliza- 

 tion of the cotton plug, and hence, prevents subsequent 

 contamination by moulds. Moreover, the serum when once 

 solidified will not dry down during the subsequent exposures 

 to heat. 



The serum tubes, sealed as above, are inclined in what is known 

 as Koch's serum sterilizer [Wig. 65). The inner compartment is sur- 

 rounded by a water-jacket. A thermometer should be placed on the 

 inside of the apparatus and another one is suspended in the water. A 



■t-r. ■ 



Fig. 64. The Roux water-bath for serum sterilization. 

 D— Wire basket with adjustable bottom E; R— Metallic COlor 

 regulator of Roux. 



then sealed 



