BLOOD-SERUM. 101 



need occur. The collecting bulb is used in the follow- 

 ing way: an artery, either femoral or carotid, is ex- 

 posed, and around it two ligatures are placed; that 

 distant from the heart is tightened, while the one near- 

 est the heart is left loose; between the latter and the 

 heart the artery is clamped. A small slit is then made 

 in its wall, into which the point a of the bulb is intro- 

 duced and the artery bound tightly around it with the 



FIG. 20. 



a 

 Nuttall's bulb for collecting blood-serum under antiseptic precautions. 



hitherto loose ligature; the clamp is removed and the 

 bulb quickly fills with blood. The clamp is now again 

 put in position, the point of the bulb removed and 

 sealed in the gas-flame, the loose ligature tightened, 

 the wound closed, and the bulb containing the blood is 

 set aside in a cool place until coagulation has occurred. 

 The serum is most easily withdrawn from the bulb by 

 means of a pipette, closed above with a cotton-plug, and 

 supplied with a bit of rubber tubing, about one-half 

 metre long, with glass mouth-piece. By holding the 



