BLOOD-SERUM. 91 



exposed, and around it tM'o ligatures are placed ; that 

 distant from the heart is tightened, while the one nearest 

 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 

 hitherto loose ligature ; the clamp is removed and the 



Fig. 17. 



o' 

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



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 vessel 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 The serum is most easily withdrawn from the bulb by 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 

 pipette in the hand and sucking upon the rubber tube 

 one can more easily direct the point of the pipette than 

 if it is used in the ordinary way. 



