378 i BACTERIOLOGY. 
oughly cleansed with hot water is taken to the slaughter- 
house and filled with freshly-shed blood from a calf or 
sheep. The blood is received directly in the jar as it 
spurts from the cut in the throat of the animal. After 
the edge of the jar has been wiped it is covered with 
the lid and set aside, where it may stand quietly until 
the blood has thoroughly clotted. The jar is then car- 
ried to the laboratory and placed in an ice-chest. If 
the jar containing the blood is carried about before the 
latter has clotted, very imperfect separation of the serum 
will take place. It is well to inspect the blood in the 
jar after it has been standing a few hours, and if the 
clot is found adhering to the sides, to separate it by a 
rod. The blood is allowed to remain twenty-four hours 
on the ice, and then the serum which surrounds the clot 
is siphoned off by a rubber tube and mixed with one- 
third its quantity of nutrient beef broth, to which 1 
per cent. glucose has been added. This constitutes the 
Léffler blood-serum mixture. This is poured into tubes, 
which should be about four inches in length and two- 
thirds of an inch in diameter, having been previously 
plugged with cotton and sterilized by dry heat at 
150° C. for one hour. Care should be taken in filling 
the tubes to avoid the formation of air-bubbles, as they 
leave a permanently uneven surface when the strum 
has been coagulated by heat. To prevent this the end 
of the pipette or funnel which contains the serum should 
be inserted well into the test-tube. About 2 c.c. are 
sufficient for each tube. The tubes, having been filled 
to the required height, are now to be coagulated and 
_ sterilized. They are placed slanted at the proper angle 
and then kept for two hours at a temperature just below 
95° C. For this purpose a Koch serum coagulator 
