8o BACTERIOLOGICAL METHODS 



a. Plate Medium 



Agar 1° grams 



Gelatin 25 grams 



Salt S grams 



Liebig's meat extract lo grams 



Dextrose lo grams 



Water (distilled) looo cc. 



Add gelatin when the agar is melted, dissolve the gelatin, add 

 the other ingredients, titrate to +2.0 per cent., filter, etc., as for 

 other media. The medium is to be clarified by adding the whites 

 of one or two eggs, well beaten in 25 cc. of distilled water, boil for 

 45 min. and filter through absorbent cotton. Do not add the 

 dextrose until after clearing. 



b. Tube Medium 



Agar 5 grams 



Gelatin 80 grams 



Salt S grams 



Liebig's meat extract S grams 



Dextrose 10 grams 



Water (distilled) 1000 cc. 



The manner of preparation is the same as for the plate medium. 

 However, the reaction is to be +1.5 instead of +2.0 per cent. 

 Without the dextrose and less salt and titrated to +i-o per 

 cent., the plate medium constitutes the ordinary nutrient agar- 

 gelatin medium which was formerly very much used because it 

 possessed the solidifying properties of agar combined with the 

 nourishing properties of gelatin. 



9. Endo Medium. — This medium is much used in testing for 

 the colon bacillus. It is variously modified by different workers 

 and it is highly important that some standard method of pre- 

 paring the medium should be adopted and adhered to. The 

 following is the method of preparation and use recommended by 

 the committee. 



Add 30 grams of powdered agar to i liter of cold water by 

 sifting slowly upon the surface of the water and allowing it to 



