130 BA CTERIOL OGY. 



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 iill 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. 



PRESERVATION OF BLOOD-SERUM. It is some- 

 times desirable to preserve blood-serum in a fluid 

 state. This can be done by the fractional method 

 of sterilization at low temperatures, already described, 

 or with much less effort, and without 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 its disinfectant 

 or antiseptic properties are no longer required. If, there- 

 fore, the serum to be preserved be placed in a closely 

 stoppered flask and enough chloroform added to form a 

 thin layer, about 2 mm., on the bottom, the serum may 

 be kept indefinitely without contamination, so long as 

 the chloroform is not permitted to evaporate. This 

 latter provision is one on which success depends. If 

 the vessel containing the mixture of chloroform and 

 serum be not tightly corked, the chloroform vapor 



