BLOOD-SERUM. 115 



gives supports on the interior of the tube to hold the 

 coagulated blood in place. Between the long narrow 

 neck and the body of the tube a constriction is formed 

 by drawing out the tube while heated. The second tube 

 also has a similar constriction about 20 cm. from its 

 mouth. 



The two tubes are now fitted together by inserting the 

 one with the long narrow neck into the second tube ; a 

 small amount of cotton being first carefully folded 

 around the neck of the first tube, so as to prevent the 

 entrance of dust. The two tubes are then fastened to- 

 gether by means of a wire twisted around the constric- 

 tion at the neck of each tube, and the apparatus is then 

 wrapped in cotton and sterilized in a hot-air sterilizer. 



Before using the apparatus the extremity of the first 

 tube is heated in the gas-flame, and by touching this 

 point with a piece of pointed glass rod it is gently drawn 

 out into a fine cannula. When the animal has been pre- 

 pared for the operation and a vessel exposed, the point 

 of the cannula is snipped off with a sterile scissors, when 

 the point of the cannula is inserted into the vessel. The 

 pressure of blood is sufficient to fill the first tube. The 

 point of the cannula is now removed from the vessel and 

 sealed in a gas-flame. The apparatus is laid aside in an 

 almost horizontal position until the blood has become 

 completely coagulated. It is then inverted and set 

 aside for the serum to separate and trickle down through 

 the narrow neck of the first tube and collect in the 

 second tube. When this has occurred, the wire holding 

 the two tubes together is unwound, and the first tube is 

 removed and the second plugged with a well-fitting 

 sterile cotton plug, when the serum may be preserved 

 in the tube for several days without danger of con- 

 tamination. 



