18 LABORATORY COURSE IN SERUM STUDY 



central incision along the neck above the trachea is made, and the 

 carotid will be found lying very close to the trachea on either side. 

 A ligature is applied distally, the artery raised on the handle of a 

 forceps and a bulldog clamp applied toward the ridge of the neck. 

 A sterile glass canula can be inserted, but we have found that 

 with a little skill it is quite easy to lift up the artery and hold it 

 by its wall with a forceps in such a way that the blood stream 

 is not blocked. The vessel is then cut, the clamp removed, 

 and by aiming the artery with the forceps in which it is held the 

 stream of blood can be directed into a sterile test tube. In this 

 way rabbits are usually bled until distinct respiratory distress 

 ensues and the stream of blood ceases, the blood coming in 

 drops. The clamp is then applied, the vessel tied and the rabbit 

 sewed up aseptically. Such a rabbit can be kept alive and 

 further used after recovery for continuation of the immunization. 



The bleeding of guinea pigs from the carotid is in every way 

 similar, though a little more difficult than the bleeding of rabbits. 

 When guinea pigs are bled, as they will be for the purpose of ob- 

 taining complement or alexin, it is necessary to do this carefully 

 in order to obtain the best results. The blood is best taken into 

 large sterile test tubes with as little violence as possible in order 

 that there may be no breaking up of blood cells with consequent 

 hemolysis. It is best to take the blood the evening before it is 

 to be used, to allow it to clot in the test tube and then to separate 

 the clot very gently from the sides of the tube. The tube should 

 then be set aside in the refrigerator at a low temperature (1-4 C.). 

 The rapidity with which complement degenerates at higher tem- 

 peratures is generally underestimated. The following day the 

 serum is pipetted away from the clot. 



Some observers believe that complement increases in potency 

 on standing for some hours on the clot. This was the con- 

 tention of Henderson-Smith, though it has recently been con- 

 tradicted by Addis and others. It is a good practice to obtain it 

 in this way, however, because blood so taken is apt to be clearer 

 and freer from haemolysis than blood centrifugalized immediately 

 after clotting. Although a slight tinge of haemolysis does not 



