98 



SOLID CULTIVATION MEDIA, 



{£.) Cultivation on Sterilised Solidified Blood Serum. 



48. Another solid and transparent cultivating medium is supplied 

 by the serum which is separated from blood after it has clotted. The 



blood of any animal will supply this, 

 but it is found that that from the calf 

 is most abundant, and has the greatest 

 degree of translucency. Having been 

 sterilised by a long process of inter- 

 rupted heating, it is solidified by care- 

 fully inspissating it at a high tempera- 

 ture. To obviate as far as possible the 

 risks of contamination from without, 

 the blood is carefully collected in pre- 

 pared jars at the period of slaughter- 

 ing. Tall stoppered glass jars (see 

 Fig. 51) are prepared for its reception, 

 by being thoroughly cleansed, first 

 with a one per cent, solution of 

 mercuric chloride, and then with 

 absolute alcohol. The stopper is 

 smeared thoroughly with vaseline containing corrosive sublimate, 

 to prevent its becoming fixed, and to exclude atmospheric dust 

 from the jar and its contents. Jars thus prepared are allowed 

 to stand in an ice - press for several hours before use ; and, 

 during the process of slaughtering, the blood is allowed to flow 

 directly from the animal's neck into a jar, unstoppered for the 

 moment for this purpose. The first gush of blood is rejected, to 

 avoid impurities which it 'might acquire in passing through the 

 wound. When the jar is filled to within two inches of the top, it is 

 re-stoppered and placed at rest in an ice-press or cool place for 

 twenty-four hours. ^ At the end of that time, coagulation and the sub- 



FlG. 51. — ^Jar for collecting 

 blood. 



' During the first few hours, a small quantity of thin and watery but deeply 

 stained fluid accumulates at the surface of the coagulated mass. This should be 

 carefully removed with a sterilised pipette, or it may discolour the serum which 

 collects around the contracting clot, and interfere somewhat with the transparency 

 of the fluid, and still more with the solidified serum. 



