42 METHODS OF CULTIVATION OF BACTEKIA 



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 Buusen below. The temperature is controlled by a gas regulator, and 

 such an apparatus can, by altering the temperature, be used either for 

 sterilisation or inspissation. 



LSffler's Blood Serum. — This is the best medium for the 

 growth of the b. diphtherise, and may be used for other organisms. 

 It has the following composition : Three parts of calf's or lamb's 

 blood serum are mixed with one part ordinary neutral peptone 

 bouillon made from veal with 1 per cent, of grape sugar added 

 to it. Though this is the original formula, it can be made from 

 ox or sheep serum and beef bouillon without its qualities being 

 markedly impaired. Sterilise as in the case of solidified blood 

 serum (p. 40). 



Alkaline Blood Serum (Lorrain Smith's Method). — To each 

 100 c.c. of the serum obtained as before, add 1 to 1*5 c.c. of a 

 10 per cent, solution of sodium hydrate and shake gently. Put 

 sufficient of the mixture into each of a series of test-tubes, and, 

 laying them on their sides, sterilise by method B (2). If the 

 process of sterilisation be carried out too quickly, bubbles of gas 

 are apt to form before the serum is solid, and these interfere with 

 the usefulness of the medium. This can be obviated if the serum 

 be solidified high up in the Koch's steriliser, in which the water 

 is allowed only to simmer. In this case sterilisation ought to go 

 on for one and a half hours. A clear solid medium (consisting 

 practically of alkali-albumen) is thus obtained, and is of value 

 for the growth of the organisms for which Koch's serum is used, 

 and especially for the growth of the b. diphtherise. Its great 

 advantage is that aseptic precautions in obtaining blood from the 

 animal are not necessary, and it is easily sterilised. 



Marmorek's Serum Media. — Marmorek succeeded in main- 

 taining the virulence of cultures of pyogenic streptococci by 

 growing them on the following media, which are arranged in the 

 order of their utility : — 



1. Human serum 2 parts, bouillon 1 part. 



2. Pleuritic or ascitic serum 1 part, bouillon 2 parts. 



3. Asses' or mules' serum 2 parts, bouillon 1 part. 



4. Horse serum 2 parts, bouillon 1 part. 



Sterile ox seruni may be used in a similar way. In the case 



