INOCULATION OF BLOOD SERUM. 103 



Second Day. — Remove serum with sterile pipette into sterile test- 

 tubes. 

 In slow steriliser at 57" C. for six hours. 

 Third Day. \ 

 Fourth ,, J 



Fifth ,, \ \n slow steriliser at 57 ' C. for four hours. 

 Sixth ,, \ 

 Seventh ,, ./ 

 Eighth Day. — In thermostat 68 ' to 80 ' C, till solid. 



Method of Inoculation. 



49. To inoculate one of the sterile tubes of serum, a mounted pla- 

 tinum wire of medium thickness is chosen, with sufficient rigidity to 

 enable it to produce a furrow on the surface of the tough serum. The 

 tip of the wire is bent at a right angle (see Fig. 21), and upon it, after it 

 has been sterilised at a white heat, is placed an infinitesimal quantity 

 of the seed material. The test-tube is held inverted, to prevent the 

 entrance of atmospheric impurities ; the cotton wool plug is then re- 

 moved, and held between two of the fingers, with its lower part point- 

 ing downwards (Fig. 34), and the loaded platinum wire is now intro- 

 duced into the test-tube. The bent point of the wire is pressed down 

 upon the surface of the solid serum, and longitudinal furrows are made 

 by drawing the wire in a series of parallel lines from the lower extremity 

 towards the mouth of the test-tube, and in this way the seed material 

 is implanted in linear tracts, along which the characteristic features of 

 the resulting growth may be observed. The wire is now withdrawn, 

 and the cotton wool plug replaced in the mouth of the tube. The 

 wire is immediately heated to a white heat, to obviate the risks of 

 disseminating the seed material, which is often of a dangerous 

 character, amongst neighbouring objects. 



The test-tubes may be placed in an incubator, and kept at blood- 

 heat, if this be desirable ; and the serum so used has this advantage 

 over peptonised beef jelly, that it retains its solidity at all tempera- 

 tures. 



Inspissated blood serum prepared in this way in sterile test-tube^ 

 has been chiefly employed in the cultivation of some organisms which 



