CHAPTER XVI 

 THE TECHNIQUE OF SERUM REACTIONS 



Obtaining Serum from Animals and Man. To obtain blood serum 

 from man, the blood may be taken from the finger or the ear, either 

 into a sterile centrifuge tube or into a Wright capsule. When taken 

 into a centrifuge tube, the blood is allowed to clot and the serum sep- 

 arated by centrifugation. Larger quantities of blood may be taken 

 with a syringe from the median basilic vein and either slanted in sterile 

 test tubes in the ice chest or put into centrifuge tubes and centrifugalized, 

 In bleeding small laboratory animals, a number of methods may' be 

 employed, depending upon the quantity of serum required. 



The animals most frequently used for laboratory purposes are rab- 

 bits. To obtain small quantities of serum from rabbits, the animals 

 may be bled from the marginal vein of the ear. The animal is strapped 

 upon a tray and underneath it is placed a rubber bag filled with warm 

 water. This is advised by Wadsworth to facilitate the flow of blood. 

 The tray is then placed upon an easel so that the animal's head hangs 

 downward. The skin over the ear vein is shaved and sterilized, and a 

 Hagedorn needle plunged into the vein. The blood is caught in test 

 tubes or centrifuge tubes. 



When larger quantities of blood are desired it may be taken from 

 the carotid artery. In rabbits, the carotid may be found lying just 

 lateral to the trachea and deeply placed, and must be carefully separated 

 from the pneumogastric nerve by blunt dissection. The distal end of 

 the artery is then tied off and the proximal end temporarily closed 

 with a small clamp. The artery is then raised out of the wound on a 

 knife or forceps handle and, with sharp-pointed scissors, a small in- 

 cision is made into but not through the vessel. A small glass cannula 

 is now introduced and tied into place by a thread. To this cannula a 

 small rubber tube fitted with a pinch-cock should have been attached, 

 the whole being sterilized. Recently we have dispensed with the can- 

 nula, simply holding the vessel up with a pointed forceps. A larger 

 yield of serum will be obtained if, after coagulation, the clot is sep- 

 arated from the glass with a sterile platinum wire. 



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