104 BACTERIOLOGICAL LABORATORY TECHNIC 



Potato Tubes. 



i. Wash some large potatoes and with a Ravenel potato cutter, 

 cut out semi-cylinders of potato. Immerse in running water over 

 night, in order to prevent them from turning black. It is well 

 to wash these bits of potato with 1-10,000 bichloride 

 of mercury 6 hours and running water over night. 

 Some laboratories soak their slices in sodium carbon- 

 ate solution. It is desirable to know the reaction 

 of the medium and each batch should be tested, then 

 marked whether faintly or strongly acid or alkalin. 



Thrust absorbent cotton to the bottom of the tube 

 and wet with distilled water; place the potato upon 

 the cotton, then plug the tube and sterilize in auto- 

 clave twice. The tubes should be sealed. 



PEPTONE SOLUTION Dunham. 



Take Peptone 10 grams 



Salt 5 grams 



Water 1,000 c.c. 



Mix. Boil. Filter and store in tubes and sterilize. 



This is used to demonstrate the production of 

 indol. 



Dextrose and lactose culture media are often 

 FIG. 28. Po- 

 tato in culture used. They are prepared by adding i percent of 



tube. (Wil- these sugars to the various media before neutraliza- 

 hams.) 



tion. 







BLOOD AGAR. 



Is prepared by adding to agar some defibrinated rabbit's blood 

 in varying proportions before the agar is tubed and hardened. 



