STERILISED BLOOD SERUM. 



99 



sequent contraction of the blood-clot are complete, and a mass of 

 fibrin containing all the red blood corpuscles is found floating in a 

 quantity of clear limpid serum, which has been extruded on the con- 

 traction of the coagulum. This clear serum must now be transferred 

 to sterile test-tubes, in each of which must be placed a quantity 

 suitable for a single cultivation experiment. This is effected by 

 means of a glass pipette. The pipette and the test-tubes, with their 

 cotton wool plugs, are previously sterilised by heating to 170° C. for 

 one hour in a hot air chamber. The jar containing the serum is 

 then unstoppered, the pipette introduced into the serum, care being 

 taken not to disturb the floating blood-clot, and 10 c.c. of the clear 

 liquid is removed, by drawing it into the bulb of the pipette by 



Fig. 52. — "Slow steriliser" for sterilising blood serum by 

 Tyndall's method, as adopted by Koch. For description see Fig. 53. 



suction. Thence it is allowed to trickle down into the lower part of 

 one of the sterile test-tubes, which is unplugged to permit of this, 



