EFFECT OF DESICCATION UPON BACTERIA 197 



of electrolytes, non- electrolytes and colloids? How are 

 these differences explained? Is the relative preserving 

 power of these different substances according to the molec- 

 ular weight theory? Explain. 



Why is a large inoculum more apt to insure growth than 

 a small inoculum? 



Note. Salt-resisting organisms can be secured by plating in agar 

 containing 10 to l7>% of salt, from butter, brine pickles, salt pork, 

 salt fish, and other salted food. Sugar-resisting organisms can be 

 obtained similarly. 



8. State the results of your experiment in full and draw 

 conclusions. Point out any practical applications that may 

 be made. 



REFERENCES 



MARSHALL: Microbiology, pp. 147-151. 



FISCHER, A.: Structure and Functions of Bacteria, pp. 5, 8-9. 



EXERCISE 20. THE EFFECT OF DESICCATION UPON 

 BACTERIA 



Apparatus. Four sterile cover-giasses ; four sterile 

 Esmarch dishes; potato knife; eighteen tubes of sterile broth. 



Cultures. B. violaceus (non-spore-producing, non-slime- 

 forming) ; slimy milk bacillus (non-spore-producing, slime- 

 forming); B. subtilis (spore-producing, non-slime-forming); 

 meat bacillus (spore-producing, slime-forming). 



Method. 1. Using a platinum needle, smear one cover- 

 glass thickly with a culture of B. violaceus, the second with 

 the slimy milk bacillus, the third with the spore-former 

 (B. subtilis) and the fourth with the spore and slime produc- 

 ing meat bacillus. 



2. Place each of these cover-glasses in separate sterile 

 Esmarch dishes and break each into five or six small pieces 

 with a sterile potato knife. 



3. Transfer a piece of each cover-glass to a tube of 

 nutrient broth after 1, 3, 7, 14, etc., days. 



