124 BACTERIOLOGY 



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 together by means of a 

 wire twisted around the constriction 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 prepared 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 contamination. 



Preservation of Blood-serum. — It is sometimes desirable 

 to preserve blood-serum' in a fiuid state. This can be done 

 by the fractional method of sterilization at low tempera- 

 tures, already described, or with much less effort, and with- 

 out the use of heat, by a method that we have found very 

 satisfactory. In the course of Kirschner's investigations 

 chloroform was shown to possess decided disinfectant 

 properties; as it is quite volatile, it is easily got rid of when 



