40 METHODS OF CULTIVATION OF BACTERIA 



Blood Serum Media. 



Koch's Blood Serum. Koch introduced this medium, and it 

 is prepared as follows : Plug the mouth of a tall cylindrical 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, preferably an ice 

 chest. The clear serum will separate from the clotted blood. 

 If a centrifuge is available, a large yield of serum may be obtained 

 by centrifugalising the freshly drawn blood. If coagulation has 

 occurred, the clot must first be thoroughly broken up. Therserum 

 obtained by such means is frequently contaminated with bacteria. 

 These can be removed by filtration through an earthenware 

 candle, and this can be rapidly effected by using 1 an arrangement 

 such as that shown in Fig. 31, 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 manipu- 

 lations, 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. It is always well to incubate it for a day at 37 C. before 

 use, to see that the result is successful. After sterilisation it is 

 "inspissated," by which process a clear solid medium is obtained. 

 " Inspissation " is an initial stage of coagulation, and is effected 

 by keeping the serum at 65 C. till it stiffens. This temperature 

 is just below the coagulation point of the serum. The more 

 slowly the operation is performed the clearer will be the serum. 

 The apparatus used for the purpose is one of the various forms 

 of serum steriliser (e.g., Fig. 8), generally a chamber with water- 

 jacket heated with a Bunsen below. The temperature is con- 

 trolled by a gas regulator, and such an apparatus can, by altering 

 the temperature, be used either for sterilisation or inspissation. 

 As is evident, the preparation of this medium is tedious, but its 

 use is necessary for the observation of particular characteristics 

 in several pathogenic bacteria, notably the tubercle bacillus. 

 Pleuritic and other effusions may be prepared in the same way, 



