BLOOD-SERUM. 117 



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 The serum is most easily withdrawn from the bulb by 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 piece 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 



Fig. 20. 



a' 



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



if it is used in the ordinary way. The bulbs are 

 easily blown, and after having been sealed at the point 

 and plugged mth cotton can be kept on hand just as 

 are sterilized test-tubes. An ordinary test-tube drawn 

 out at the bottom to a fine point may be substituted 

 for the pear-shaped bulb with equally satisfactory 

 results. 



It is sometimes desirable to preserve blood-serum in 

 a fluid state. This can be done by the fractional method 

 of sterilization at low temperatures, already described, 



