50 METHODS OF CULTIVATION OF BACTERJA. 



use, to make certain that they are sterile. Agar poured 

 out in a thin layer in a Petri dish may be smeared with 

 blood in the same way and used for cultures. 



Peptone Solution. 



A simple solution of peptone (Witte) constitutes a 

 suitable culture medium for many bacteria. The peptone 

 in the proportion of 1-2 per cent, along with .5 per cent 

 NaCl is dissolved in distilled water by heating. The fluid 

 is then filtered, placed in tubes and sterilised. The re- 

 action is usually distinctly alkaline, which condition is 

 suitable for most purposes. For special purposes the 

 reaction may be standardised. In such a solution the 

 cholera vibrio grows with remarkable rapidity. It is 

 also much used for testing the formation of indol by a 

 particular bacterium ; and by the addition of one of the 

 sugars to it the fermentative powers of an organism may 

 be tested. Litmus may be added to show any change in 

 reaction. 



Litmus Media. To any of the above media litmus 

 (French, tournesol) may be added to show change in re- 

 action during bacterial growth. The litmus is added, 

 before sterilisation, as a strong watery solution in sufficient 

 quantity to give the medium a distinctly bluish tint. 

 During the development of an acid reaction the colour 

 changes to a pink and may subsequently be discharged. 



Blood Serum. 



Koch introduced this medium, and it is prepared as 

 follows : Plug the mouth of a tall cylindrical glass vessel 

 (say a 1000 c.c. measure) 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 sub- 



