CHAPTER XI 



STUDY OF CERTAIN CHROMOGENIC BACTERIA 

 EXERCISE I. CULTURAL STUDIES 



1. Read carefully the following references to chromo- 

 genic organisms, and the production and chemistry of 

 pigments: 



Sternberg, Manual of Bacteriology. 

 Lehmann and Neumann. 



Members of this group are widely disseminated in the 

 air, water, etc. A few representatives will be studied. 



2. Inoculate agar-slants from stock-cultures of Bacil- 

 lus prodigiosus, B. pyocyaneus, B. violaceus, and Sarcina 

 luiea. Inoculate three slants each of B. prodigiosus and 

 B. pyocyaneus, and one each of Sar. lutea and B. violaceus. 



3. Label each tube with the name of the culture 

 inoculated, the date of the stock-culture and the date of 

 inoculation. Place the label on the side of the tube 

 where the slanted surface of the medium is. It is then 

 possible to study the growth and see the label at the same 

 time. Glass pencils for marking are very convenient. 



4. Place one culture of each organism in the thermo- 

 stat, one culture of B. prodigiosus and B. pyocyaneus in 

 the locker, and leave the others exposed to sunlight. 



5. After 24 hours compare the growths of B. prodigio- 

 sus and B. pyocyaneus, under the various conditions, in 

 respect to 



a) Relative amount of growth. 



b) Relative amount of pigment produced. 



What conclusions can be drawn from this experiment ? 

 69 



