16 LABORATORY COURSE IN SERUM STUDY 



some extent on the health of the animal, the size of the injec- 

 tions, and the intervals. It is a safe rule to assume that the 

 high point in the curve is apt to lie between the eighth and the 

 twelfth day after the last injection and to be guided by this in 

 preliminary titrations. 



THE BLEEDING OF ANIMALS 



Before the immunization of the animal is begun a sample of 

 blood should be taken from the ear vein of the animal and the 

 serum stored in the refrigerator for use as a control at a later exer- 

 cise when the serum of this animal is tested for immune bodies. 

 The blood can be obtained from the marginal vein in the ear in 

 the following manner. 



The animal is firmly held with the head down by an assistant. 

 The lateral portion of the hairy surface of the ear is carefully 

 shaved and the skin rubbed vigorously to cause the veins to dis- 

 tend. If necessary the ear may be rubbed with xylol. The skin 

 over the vein is washed over with alcohol and a cut made in the 

 vein with a razor blade or other sharp instrument. The blood is 

 allowed to drip into a clean centrifuge tube until about 4 c.c. 

 (60 drops) are obtained. It is then allowed to coagulate and the 

 edges of the clot are freed from the side of the tube by means of a 

 sterile platinum wire. The tube is centrifugalized and the clear 

 serum thus expressed is transferred to a sterile test tube by 

 means of a capillary pipette with a rubber nipple attached. It is 

 then labelled carefully and stored in the icebox for future use. 



Later bleeding from the ear veins of a rabbit can be facilitated 

 by strapping the animal down on a flat, hot water bag. A techni- 

 cal point of great simplicity but which helps to make the sort of 

 cut in the vein which favors free bleeding, consists in taking a 

 pointed steel writing pen, breaking off one of the prongs and 

 plunging the stilette thus made straight into the vein in a direc- 

 tion toward the heart. The entry thus made through the wall 

 of the vein does not easily collapse and very free bleeding results. 



To bleed a rabbit from the carotid the rabbit is strapped down 

 on its back on a dissecting board and ether administered. A 



