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. (See section 

 on Opsonins, page 284.) When taken into a centrifuge tube, the 

 blood is allowed to clot and the serum separated from the coagulum by 

 a few revolutions of the centrifuge. When larger quantities of blood 

 are desired, it 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 centrifugaUzed. 



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

 employed, depending upon whether a large or small amount of serum is 

 required. 



The animals most frequently used for laboratory purposes are 

 rabbits. To obtain small quantities of senun from rabbits, the animals 

 may be bled from the marginal vein of the ear. In doing this, a satis- 

 factory yield of blood may be obtained by following a simple method 

 devised by Wadsworth. The animal is strapped upon a tray and under- 

 neath it is placed a rubber bag filled with warm water. This keeps the 

 body temperature of the rabbit somewhat higher than normal, causes 

 dilatation of the vessels, and thus faciHtates the flow of blood. The 

 tray is then placed upon a simply constructed easel so that the animal's 

 head hangs downward. The skin over the ear vein is shaved and 

 sterihzed, and an incision is made into the vein in its long axis with a 

 sharp knife. The blood is caught in test tubes or centrifuge tubes. 



When larger quantities of blood are desired, the animal is strapped 

 down, anesthetized, and the neck shaved and sterilized. The carotid 

 artery is then isolated by dissection. In rabbits, the carotid artery 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 tem- 

 porarily closed with a small clamp. (This clamp should be rather weak 

 and not exert sufficient pressure to injury the artery and cause throm- 



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