ALBUMINOUS MEDIA 



45 



3. Media made from albuminous fluids and tissues. 



Serum. 



Serum is the liquid which separates when blood has clotted. In bacteriology 

 bovine, sheep and horse serum are principally used. Serum is most frequently 

 used after coagulation by heat, very rarely in the liquid condition. 



An important point about serum media is that they should be almost 

 transparent, hence they cannot be heated to a high temperature because 

 they coagulate en masse and become opaque. Liquid serum ought net to 

 be heated above 56 or 58 C., and to preserve its transparency solidified 

 serum should be coagulated at about 70 C. 



Serum cannot therefore be sterilized in the ordinary way. 



Either (a) it must be sterilized by pasteurization combined with tyn- 

 dallization (Koch's method) or by filtration through a bougie : or (b) since 

 the blood in the body is sterile, a sterile medium can be obtained if care be 

 taken to avoid introducing contaminations while collecting the blood and 

 drawing off the serum (Roux and Nocard's method). 



Collection of serum. 

 1. In the slaughter-house. 



[A. Method recommended. When the blood is collected in the slaughter- 

 house, the following is a simple method of proceeding. 



[1. When the carotid is severed discard the first spurt of blood, then take 

 the plug out of a sterile 2-litre flask and hold it so that the blood pours 

 into the open mouth : collect enough blood to three-parts fill the flask : 

 replace the plug. Collect as many flasks of blood as are required. 



[2. On reaching the laboratory place the flask on a cork ring, inclining it 

 as much as possible. Take out the wool plug, burn the mouth of the flask 

 with a Bunsen burner both inside and outside and plug the flask at once 

 with clean wool ready sterilized and wrapped in paper. Then stand the 

 flask vertically, shaking it as little as possible. 



FIG. 33. Cobbett's bulb as used for decanting serum. 



[3. When the clot has formed and the serum separated, tilt the flask again 

 the clot should adhere to the bottom and introduce a piece of glass 

 tubing connected to a Cobbett's bulb (fig. 33). 



