PREPARATION OF NUTRIENT MEDIA. 8? 



vated on solid blood serum. This medium has the 

 additional advantage of remaining solid at all tem- 

 peratures. The technique required for its preparation 

 and sterilisation is as follows : Several cylindrical 

 vessels, about 20 cm. high, are thoroughly washed 

 with sublimate solution (i-iooo), and then with 

 alcohol, and finally rinsed out with ether. The 

 ether is allowed to evaporate, and the vessels are 

 then ready for use. The skin of the animal 

 selected calf, sheep, or horse is washed with 

 sublimate at the seat of operation, and the bleeding 

 is performed with a sterilised knife. The first jet 

 of blood from the vein is rejected, and that which 

 follows is allowed to flow into the vessels until 

 they are almost full. The ground-glass stoppers, 

 greased with vaseline, are replaced, and the vessels 

 set aside in ice, as quickly as possible, for from 

 twenty-four to thirty hours. By that time the 

 separation of the clot is completed, and the clear 

 serum can then be transferred to plugged sterile 

 test-tubes. These should be filled with a sterilised 

 pipette for about a third of their length, and are 

 then placed in Koch's slow steriliser with the tem- 

 perature maintained for an hour at 58 C. The 

 same process is repeated for six successive days, 

 the temperature on the last day being gradually 

 raised to 60. This completes the sterilisation, but 

 to solidify the serum it is necessary to arrange the 

 tubes in the inspissator at the angle required. The 

 temperature of this apparatus is kept between 65 



