62 A MANUAL OF BACTERIOLOGY 



place for two or three days to make sure that they are 

 sterile, those in which a growth appears being rejected. 



Serum, ascitic fluid, etc., may also be obtained sterile 

 by filtering through a sterilised Berkefeld filter into sterile 

 flasks. 



Serum, ascitic and hydrocele fluids, etc., may be pre- 

 served in bulk and used as required. The material is 

 collected as aseptically as possible, 5 per cent, of chloro- 

 form is added, and the whole is well mixed and kept in a 

 cool place in the dark in a well-stoppered bottle. Sub- 

 sequently, during the process of sterilisation, the chloroform 

 is volatilised. 



Serum agar (Kanthack and Stevens). Ascitic, pleuritic, 

 or hydrocele fluid is collected in clean (not necessarily 

 sterilised) flasks, and allowed to stand overnight in a cool 

 place to allow the sediment or blood to deposit. The 

 clear fluid is then poured off, and to each litre enough 

 of a 10 per cent, caustic potash solution is added to render 

 it very distinctly alkaline usually about 2 c.c. to every 

 100 c.c. of the fluid. The alkaline fluid is heated in the 

 autoclave for two to four hours. To this fluid 1-5 to 2 per 

 cent of agar is added, and the mixture is heated until the 

 agar dissolves. It is then filtered, introduced into test- 

 tubes, sterilised, and solidified in the ordinary way. The 

 addition of 5 per cent, of glycerin and 1 per cent, of glucose 

 is an advantage. 



Serum agar may also be prepared by adding sterile 

 serum or hydrocele or ascitic fluid, warmed to 45 C., 

 to sterile nutrient agar (2 to 3 per cent, agar) melted and 

 cooled to 45 C. Equal parts of the serum and agar may 

 be mixed, or 1 part of serum to 2 parts of agar. 



Blood agar. This may be prepared by smearing the 

 surface of the agar in sloping agar-tubes with blood 

 obtained aseptically from the finger or from a rabbit. 

 Or blood obtained aseptically may be defibrinated by 



