SERUM 51 



4. When the clot has formed and shrunk from the pieces of glass tubing, 

 invert the bottle gently in its support so that the neck is the lowest part. 

 The serum will then run down into the neck. 



5. Clip the tubing at p, break off the pointed end of the glass tubing, and 

 plunge it into the sterile flask in which the serum is to be collected : loosen 

 the clip, and the serum will flow out. By means of the clip the rate of flow 

 can be altered at will or entirely stopped. 



The opening of e within the bottle being a little distance from the plug, a small quantity 

 of serum containing red cells remains in the bottle ; the bend in the tube prevents these 

 cells from being drawn off with the serum. 



Coagulation of serum. 



Serum is coagulated by heat. In order that it may retain its transparency, 

 the temperature during coagulation must not exceed 68-70 C., and to 

 completely solidify the serum it must be kept at this temperature for 

 2 or 3 hours. 



The tubes containing the liquid serum are sloped as in the case of agar. 

 Coagulation is generally effected in a modified form of the apparatus devised 

 by Koch [e.g. in an Hearson's serum coagulator.] 



[Hearson's serum coagulator. In construction and in some models in 

 appearance Hearson's serum coagulator (fig. 41) is the same as Hearson's 



FIG. 41. Hearson's apparatus for the coagulation of serum. 



warm (37 C.) incubator (p. 61), but in the former the capsule is constructed 

 to work at higher temperatures such as are suitable for the coagulation of 

 serum. Special holders are also supplied which retain the tubes in a slant- 

 ing position. To maintain a saturated atmosphere, dishes of water or wet 

 cloths can be placed on the floor of the coagulator.] 



Koch's apparatus consists of a double- walled rectangular copper box supported 

 on legs, by means of which the angle which it subtends with the horizon can be 

 altered at will. The space between the walls is filled with water, and the floor of 

 the apparatus is covered with a thin layer of sand on which the tubes are laid. A 

 thermometer is placed alongside the tubes. The apparatus is closed above with 

 a moveable cover consisting of two sheets of glass mounted in a metal frame with 

 a thin layer of air between them. The apparatus is heated by gas, which passes 

 through a Roux's regulator immersed in the water between the two walls. The 

 technique is as follows : 



