GUARNIARI'S OELATIN-AGAR MIXTURE 131 



levulose, mannite, etc., is then added in the proportion of 

 1 per cent. The finished medium is then placed in test- 

 tubes. The medium must be sterihzed in an Arnold steam 

 sterilizer, and it is advisable to allow the sterilizer to 

 remain uncovered during the process of sterilization to avoid 

 excessive heating of the medium. 



The relative degree of acidity produced, with or without 

 coagulation, with or without gas-production, and with or 

 without reduction of the litmus, in a series of tubes of this 

 medium containing the different carbohydrates serves to 

 differentiate between related species of bacteria. For 

 instance, the colon bacillus produces an acid reaction with 

 coagulation and gas-formation with some of the carbohy- 

 drates, while the typhoid bacillus produces a lower degree 

 of acidity with coagulation, but without gas-production. 

 Similariy, the different tj-pes of the dysentery bacillus may 

 be differentiated by means of their effects on the different 

 carbohydrates in this medium. 



GUARNIARI'S GELATIN-AGAR MIXTURE. 



For special work, particulariy with the organism of pneu- 

 monia (bacterium pneumoniae) the gelatin-agar mixture 

 recommended by Guarniari is of very great service. It 

 should be exactly neutral in reaction, and should possess 

 the following ingredients : 



Meat infusion . 950 c.c. 



Sodium chloride . 5 grams 



Peptone 25 to 30 grams 



Gelatin 40 to 60 grams 



Agar-agar 3 to 4 grams 



Water . . . 50 c,c. 



