DETERMINING BIOLOGICAL ACTIVITIES OF BACTERIA 205 



complement in Wassermann reactions, this is among the best 

 methods since large guinea pigs can be alternately bled and rested. 

 Both in rabbits and guinea pigs, bleeding directly from the heart 

 is easily accomplished after a little practice. The anterior thorax 

 of the animal is clipped and painted with tincture of iodin and the 

 operator in feeling for the third interspace close to the sternum 

 had best paint the tips of his fingers with iodin. A twenty-two 

 gauge needle about two inches long is then attached to a syringe 

 and passed downward in the third left interspace close to the 

 sternum, slight suction being exercised at the same time. There 

 is not much purpose in describing this in detail since it can be 

 taught only by practice. 



Both rabbits and guinea pigs can be bled from the carotid. The 

 animal is anesthetized as above, and the carotid laid bare. It is 

 found vety close to the trachea, in rabbits lying almost in contact 

 with the trachea, and a little behind it. It is carefully separated 

 from the vagus nerve, and tied off in its distal portion. The thread 

 with which it is tied can be used to handle it thereafter. A sterile 

 glass cannula can be thrust into the artery and the blood taken 

 through this, or else, as we prefer to do it, the side of the artery 

 is picked up with a very fine forceps and held with one hand while 

 it is cut across with a sharp scissors. In this way the blood can 

 be directed straight into a wide mouth flask without being allowed 

 to come in contact with anything until it hits the inside of the flask. 



Larger animals, like sheep, goats, horses, are. easily bled by 

 plunging a sterile needle into the external jugular vein which runs 

 in these animals from a line just behind the angle of the lower jaw 

 to the sterno-clavicular junction. 



The blood can be run directly into media as for blood agar, blood 

 broth and chocolate medium. 



If serum is desired, it can be run into containers of various kinds 

 slanted and allowed to clot in the ice-box. 



If defibrinated blood is desired, the blood can be taken directly 

 into sterile flasks containing pieces of broken glass or beads and 

 attenuated before clot. Such blood can be kept in the ice-chest and 

 added to media subsequently. 



Blood can be also preserved for culture purposes by the addition 

 of just enough ether to hemolyze it, and added to media in this 

 form. The ether is evaporated off. 



