BLOOD SERUM. 43 



Peptone Solution or Dunham's Medium. 



A simple solution of peptone (Witte) constitutes a suitable 

 culture medium for many bacteria. The peptone in the propor- 

 tion of I to 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 reaction is usually distinctly alka- 

 line, 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. 



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^iilled. 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 care- 

 fully back to the laboratory without shaking, and place for 

 twenty-four hours in a cool place, preferably an iccrchest.- The 

 ■clear serum will separate from the clotted blood. If a centrifuge 

 is available,,, a large yield of serum may b^ obrained Isy centrifu- 

 gaHsingtljg^eshly drawn blood. If coagulation has occurred., 

 the clot rftfe- first be thoroughly broken up. With; a sterile 

 10 c.c. pipette transfer this quantity of serum to each of a series 

 ;i!pf test-tubes which must previously have been sterilised by dry 

 ; %eat. The serum may, with all precautions, have been con- 

 taminated 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," 



