268 APPENDIX 



needed for their neutralization, and acid media with the 

 plus (+) sign before the percentage of normal alkaline 

 solution necessary for their neutralization. 



The standard reaction of culture media shall be +1.0 

 per cent. If it differs from i per cent by more than 0.2 

 per cent it should be readjusted. 



Wherever reactions other than the standard above given 

 are used it shall be clearly stated in all results of bacterial 

 work, and the reasons therefor also stated. 



STORAGE OF MEDIA 



It is recognized by the committee that it is desirable 

 to prepare media in large quantities in order to guard 

 against discrepancies in composition; but, all things con- 

 sidered, the complications resulting from the varying 

 amounts of heating incident to withdrawing portions from 

 time to time and tubing it, are believed to more than 

 offset this advantage. Consequently, when possible, media 

 shall be put at once into tubes and placed in cold storage. 



To guard against changes due to evaporation all media 

 not used promptly shall be stored in a moist atmosphere, 

 preferably in an ice-box, or else the flask shall be sealed 

 by dipping the cotton plug in paraffin. 



NUTRIENT BROTH 



Nutrient broth shall be prepared as follows: Infuse 

 500 gm. chopped lean meat 24 hours with 1000 c.c. dis- 

 tilled water in refrigerator. Restore loss by evaporation. 

 Strain infusion through cotton flannel. Add i per cent 

 peptone. Warm on water bath, stirring until the pep- 

 tone is dissolved. Heat over boiling water (or steam) 

 bath 30 minutes. Restore loss by evaporation. Titrate. 

 Adjust reaction to -fi per cent by adding normal hydro- 

 chloric acid or normal sodium hydrate, as required. Boil 



