468 BACTERIOLOGY. 



Chapter XV). When inclined serum is wanted the tubes are 

 placed in the coagulating apparatus (Fig. 65), and heated 

 for about 1 hour at 70°. They are then ready for use. 

 Lafler's blood-serum and glycerin serum must be heated to 

 about 75° in order to insure perfect coagulation. Obviously, 

 the blood-serum tubes may be inclined in the ordinary dry- 

 heat sterilizer (Pig. 25) and solidified at 70°, or at a higher 

 temperature. 



Loffler's blood-serum. — This medium is chiefly employed 

 for cultivating the diphtheria bacillus. It is prepared by 

 adding to three parts of blood-serum, one part of ordinary 

 bouillon to which 1 per cent, of glucose has been added. 

 The mixture is then sterilized according to one of the metji- 

 ods outlined above. It is finally coagulated in an inclined 

 position. It should be remembered that Loffler's serum re- 

 quires more time and a higher temperature to secure coagu- 

 lation than does ordinary serum. 



Glycerin blood-serum. — This is prepared by merely adding- 5-6 per 

 cent, of glycerin to the blood-serum. This mixture is then sterilized 

 and inclined according to the directions given above. ' 



Boiled nor}rcoagulated serum. — When serum is diluted with 5 to 10 

 parts of distilled water it can be sterilized by steaming without 

 undergoing coagulation. This albuminous liquid -can be utilized to 

 advantage in some cases. 



Oxalate blood or plasma.— The preparation of this medium is de- 

 scribed on p. 4§3. 



Filtration of Bacterial Liquids. 



A liquid, may be deprived of the bacteria which are 

 present by filtration through unglazed porcelain. The 

 Pasteur-Chamberland bougie is by far the most reliable for 

 this purpose. As stated on p. 464 the walls of the bougies 



