BLOOD SERUM MEDIA 



41 



Sufficient sterile J 8 per cent, sodium chloride is added to each 

 tube to cover the medium in the upright position. The tubes 

 are then sterilised in this position in the autoclave for a quarter 

 of an hour at 115° C. and thereafter stored. When a tube is 

 to be used the saline is poured off. The advantages of this 

 method are that com- 

 plete sterility is readily 

 obtained and the medium 

 does not dry up. 



Koch's Method. — Plug 

 the mouth of a tall cylin- 

 drical glass vessel (say of 

 1000 c.c. capacity) with 

 cotton wool, and sterilise 

 by steaming it in a Koch's 

 steriliser for one and a half 

 hours. Take it to the place 

 where a horse, ox, or sheep 

 is to be killed. When the 

 artery or vein of the animal 

 is opened, allow the first 

 blood which flows, and 

 which may be contaminated 

 from the hair, etc., to 

 escape ; fill the vessel with 

 the blood subsequently shed. 

 Carry carefully back to the 

 laboratory without shaking, 

 and place for twenty-four 

 hours in a cool place, pre- 

 ferably 'an ice chest. The 

 clear serum will separate 

 from the clotted blood. 

 The serum obtained by such 

 means is frequently con- 

 taminated with bacteria. 

 These can be removed 

 by filtration through an 

 earthenware candle, and 

 this can be rapidly effected 

 by using an arrangement 

 such as that shown in" 

 Fig. 27, the serum during filtration being kept at about 55° C. With a 

 sterile 10 c.c. pipette, transfer this quantity of serum to each of a series 

 of test-tubes which must previously have been sterilised by dry heat. 

 The serum may, with all precautions, have been contaminated during the 

 manipulations, and must be sterilised. As it will coagulate if heated 

 above 68° C, advantage must be taken of the intermittent process of 

 sterilisation at 57° C. [method B (4)]. It is therefore kept for one hour 

 at this temperature on each of eight successive days. The medium 

 should be incubated for a day at 37° C. before use, to see that the result 



8. — Blood serum inspissator. 



