BLOOD-SERUM. 97 



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 introduced 

 and the artery bound tightly around it with the hitherto 

 loose ligature; the clamp is removed and the bulb 



FIG. 17. 



a 

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



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 serum is most easily withdrawn from the bulb by means 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 sup- 

 plied 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. 



The bulbs are easily blown, and after having been 



