50 METHODS OF CULTIVATION OF BACTERIA. 



the serum is solid, and these interfere with the use- 

 fulness 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 practi- 

 cally 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. diphtherise. Its great advantage is that aseptic pre- 

 cautions 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 

 with i-iooo corrosive sublimate, and a piece of circular 

 filter paper, moistened with the same, is laid in its bottom. 

 On this latter are placed four sterile watch glasses. Two 

 firm, healthy, small, round potatoes, as free from eyes as 

 possible, and with the skin whole, are scrubbed well with a 

 nail brush under the tap and steeped for two to three hours 

 in i-iooo corrosive sublimate. They are placed in a 



