PHYSICAL PRODUCTS OF METABOLISM 177 



2. At the end of seven days test the reaction of each. Is 

 there any relation between the reaction and pigment pro- 

 duction? 



3. What conditions are conducive to the formation of 

 red milk? of blue milk? 



How would you describe and explain " bloody " milk as 

 produced by microorganisms to anyone unfamiliar with the 

 phenomenon? How differentiated from true bloody milk? 



4. State all results in full. Draw any conclusions war- 

 ranted and point out the practical applications that may be 

 made. 



REFERENCES 



LAFAR: Technical Mycology, Vol. I, pp. 105-122. 



THRESH: Examination of Waters and Water Supplies, 2d Edition, pp. 



43-44. 



STERNBERG: Textbook of Bacteriology, pp. 130-132. 

 CONN: Agricultural Bacteriology, pp. 156-157. 



EXERCISE 10. TO ILLUSTRATE ONE OF THE PHYSICAL 

 PRODUCTS OF METABOLISM 



Apparatus. Three gelatin slants (20 alkaline, 3% salt) ; 

 rubber stopper to fit one of the gelatin tubes. 



Culture. Ps. lucifera or some actively phosphorescing 

 organism. 



Method. 1. Make a streak culture of the above organ- 

 ism upon each of the gelatin slants. 



2. With one of the cultures, boil a rubber stopper and 

 insert in place of the cotton plug. 



3. Place the stoppered culture and a second one (cotton- 

 plugged) at 20 C., the third cotton-plugged culture at 

 5-10 C. 



4. Examine in the light and in the dark after twenty-four 

 and forty-eight hours. Compare (in the dark) the two 

 cultures at 20 C.; if there is a marked difference, loosen the 

 rubber stopper and note what happens. 



5. If there is no immediate result from loosening the 



