2 1 6 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 HC1 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 J 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. 



