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. 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. 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. " Inspissa- 

 tion " is probably 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, 

 and used as media, but care must be taken in their use, as we 

 have no right to say that pathological effusions have the same 

 chemical composition as normal serum. 



If blood be collected with strict aseptic precautions, then 



