2i6 Appendix. 



Litmus Solution. — To one-half pound of litmus cubes 

 add enough water to more than cover; boil, and decant 

 off the solution. Repeat this operation with successive 

 small quantities of water until from 3 to 4 liters of water 

 have been used and the cubes are well exhausted of color- 

 ing matter. Pour the decantations together and allow 

 them to settle over night. Siphon off the clear solution. 

 Concentrate to about i liter and make the solution de- 

 cidedly acid with glacial acetic acid. Boil down to about 

 one-half liter and make exactly neutral with caustic soda 

 or potash. To test for the neutral point, place one drop of 



N 

 the solution in a test tube. One drop of — HCl should 



20 



N 

 turn the drop red, while one drop of — NaOH should 



20 



turn it blue. Filter the solution and sterilize at 110° C. 



This solution should be added to the media just before 



use in the proportion of about \ c.c. to 5 c.c. of medium. 



For the methods of preparation of other special 



culture media the student is referred to the papers 



published by the investigators who have originated the 



media in question. 



