SERUM MEDIA. 53 



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

 each 100 c.c. of the serum obtained as before, add 1-1.5 c - c - 

 of a 10 per cent solution of sodium hydrate and shake it 

 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. Dr. Smith informs us that 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-albumin) is thus obtained, and he has found it of 

 value for the growth of the organisms for which Koch's 

 serum is used, and especially for the growth of the B. 

 diphtherias. 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. There has always been a 

 difficulty in maintaining the virulence of cultures of the 

 pyogenic streptococci, but Marmorek has succeeded in 

 doing so by growing them on the following media, which 

 are arranged in the order of their utility : 



1. Human serum 2 parts, bouillon i part. 



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



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



4. Horse serum 2 parts, bouillon i part. 



Human serum can be obtained from the blood shed in 

 venesection, the same precautions being taken as in the 

 case of that got in the slaughter-house. In the case of 

 these media, sterilisation is effected by method B 4, and 

 they are used fluid. 



Potatoes as Culture Material. 



(a) In Potato Jars. The jar consists of a round, shallow, 

 glass vessel with a similar cover (vide Fig. 9). It is washed 



