Journal of Applied Microscopy. 



303 



Flowing steam is perhaps preferable to the autoclave, inasmuch as chemical 

 changes are less likely to occur at 100°C. than at higher temperatures. It is 

 best to make certain that the sterilizer is full of steam before putting the tubes 

 into it, otherwise the prolonged gradual rise from the cold water temperature 

 (which is likely to vary in different cases) to the boiling point introduces 

 another, although minor, discrepancy. Similarly, the media should not be left in 

 the sterilizer to cool down for indefinite periods. It is best to turn out the ^as 

 and remove the media as soon as the fifteen minutes sterilization is accom- 

 plished. Nutrient gelatin tubes should be plunged at once into ice water to 

 ensure the maintenance of a high melting point. A melting point of 25°C. can 

 thus be uniformly obtained without difficulty for 10 per cent, gelatin. 



The use of prepared extracts of meat is steadily giving way to the use of 

 meat infusions; these methods may, however, be adapted to their use also. 

 Perhaps the simplest adaptation is the following : 



Mix thoroughly the white of one egg with 1000 cc. water (for nutrient broth 

 and gelatin) or of one egg to 500 cc. water (for nutrient agar). Proceed then, 

 beginning with Step No. 5, exactly as given in the table, substituting " white of 

 egg solution " for " infusion " wherever the latter term occurs, but at Step No. 

 7 add also 0.5 per cent, of Liebig's extract for nutrient broth or gelatin, or 

 1.0 per cent, for nutrient agar. This proceeding will result in a liter of each 

 medium. 



The titrations necessary are made by Fuller's method. Phenolphtalein is 

 used as the indicator : " + indicates acid ; ~ indicates alkaline." 



The methods of titration, and the reasons for the adoption of these methods 

 are given in the following : 



Journal American Public Health Association, October, 1805. 

 Massachusetts State Board of Health Report, 1895 (Fuller and 



Copeland). 

 Journal American Public Health Association, January, 1898. 



Table Showing Analogy Between Broth, Nutrient Gelatin, and Nutrient Agar, 

 Made by Methods Herein Recommended. 



NUTRIENT broth. 



nutrient gelatin. 



Boil thirty grams thread agar in 

 one liter of water for half an hour. 

 Make up loss by evaporation to a 

 weight of looo grams. Cool and 

 solidify. 



nutrient agar. 



1. Infuse lean meat twenty hours 



with twice its weight of dis- 

 tilled water in refrigerator : 

 Say looo grams meat, 

 2000 grams water. 



2. Make up weight of meat in- 



fusion (and meat) to origi- 

 nal weight by adding water, 

 i. e., to 3000 grams. 



Ditto. 



Ditto. 



Infuse lean meat twenty hours 

 with //j 07v>/ weight of distilled 

 water in refrigerator. 



Say 1000 grams meat. 

 1000 grams water. 



Ditto. 



i. e., to 2000 grams. 



