ACIDS FORMED FROM CARBOHYDRATES 167 



point out any conclusions that may be drawn. Mention 

 any practical applications to be made. 



REFERENCES 



EYRE: Bacteriological Technic, 2d Ed., pp. 236-247. 

 MARSHALL: Microbiology, pp. 93-98, 228-232, 306-331, 634-640. 

 BESSON: Practical Bacteriology, Microbiology and Serum Therapy ,- 



pp. 87-105. 

 GILTNER: Suggestions for partial anaerobic cultures. Science, n. s., 



Vol. XLI, No. 1061, p. 663. 



EXERCISE 3. TO DEMONSTRATE THAT ACIDS ARE 

 FORMED FROM CARBOHYDRATES BY BACTERIA 



Apparatus. Three tubes of sterile litmus lactose agar; 

 three tubes of sterile dextrose agar containing CaCO 3 ; 

 sterile dilution flask (containing about 150 c.c. sterile salt 

 solution) ; six sterile Petri dishes-; sterile 1 c.c. pipettes. 



Culture. Fresh milk culture of Bad. lactis addi. 



Method. 1. Place a very small loopful of the Bad. lactis 

 addi culture in the dilution flask. (Transfer from the white 

 portion of the litmus milk culture.) Shake well. . 



2. Make three plates from each medium, using widely 

 varying amounts, for example, 0.5 c.c., 0.1 c.c. and 1 drop. 

 Just before plating, mix the CaCOs well with the agar (avoid 

 air bubbles). 



3. Place the plates (inverted) at room temperature. 



4. Examine each daily after forty-eight hours. Note 

 how each medium is changed by the growth of the colonies. 

 Explain what has happened. 



How is the object of the experiment demonstrated in 

 the case of each medium? 



6. Compare the size of colonies on the different media; 

 also on each dilution of one medium; explain. Why are 

 the colonies smaller on the thickly seeded plates? 



6. Write the chemical equation with a specific enzyme 

 for each change in the case of each medium. 



