Appendix. 211 



sium nitrate by dissolving four grams of solid nitrate in 

 100 c.c. of distilled water and use five c.c. of this solution 

 in the above formula. Ten c.c. of the medium thus 

 prepared shall be placed in a test tube and sterilized in 

 the usual way. 



BROTH FOR INDOL TEST. 



Standard broth may be used for the indol test if pre- 

 cautions are taken to remove the muscle sugar, by inocu- 

 lating the beef infusion with B. coli before making the 

 broth. 



Pepton solution (one per cent pepton in water), how- 

 ever, is preferred by some for use in the indol test, and 

 is considered generally to be satisfactory. Sodium nitrite 

 (o.oi per cent) shall be added in all cases. 



APPARATUS. 



Few definite requirements need be made respecting 

 apparatus. The quality of the glass shall be such as not 

 to be easily acted upon by the reagents used, and all 

 glassware shall be scrupulously clean when used. When 

 necessary it shall be sterilized by dry heat for one hour 

 at about 150 C. A slight browning of the cotton stop- 

 pers is a good index of proper exposure. 



In some operations, as, for example, the determination 

 of the thermal death point, it is necessary to use test 

 tubes of a definite size and thickness. For this purpose 

 the standard size culture tube shall be 15 cm. long, 1.6 cm. 



