CHEMICAL AGENCIES ON MICROBIAL PIGMENT 175 



7. Give your results in full. Draw any conclusions 

 possible and point out any practical applications that may 

 be made. 



REFERENCES 



LAFAB: Technical Mycology, Vol. II., Part 2, pp. 558-560. 

 MARSHALL: Microbiology, pp. 113-117. 



LOHNIS: Laboratory Methods in Agricultural Bacteriology, pp. 42, 116. 

 EYRE; Bacteriological Technic, 2d Ed., 1913, pp. 290-291. 



EXERCISE 9. THE EFFECT OF PHYSICAL AND CHEM- 

 ICAL AGENCIES ON MICROBIAL PIGMENT AND 

 THEIR FORMATION 



Apparatus. Six tubes of gelatin; six dextrose agar slants 

 + 15; eight tubes of plain milk, sterile; hydrochloric acid; 

 sodium hydroxide; chloroform; ether; benzol; carbon 

 bisulphide; litmus paper; clean slide; small funnel. 



Cultures. Ps. pyocyanea; R. violaceus; B. prodigiosus; 

 Sarcina lutea; Torula rosea; B. cyanogenus; Bad. lactis acidi. 



Method. A . Effect of temperature on pigment formation. 



1. Make two dextrose agar streak cultures of each 

 organism. 



2. Place the cultures in duplicate at 25 C. and 37 C. 



3. Examine every day or so and at the end of a week 

 record the degree of pigment formation by + +, +, H , . 

 Brightness of pigment formation should be considered in all 

 cases, not the amount of growth. 



4. Where is the pigment seen macroscopically in each 

 case? Explain. 



Does temperature have any influence on pigment forma- 

 tion? Does this correspond in each case with that of the 

 natural habitat of the organism? 



How do these several pigments differ? Of what impor- 

 tance is pigment production? 



B. Relation of air to pigment formation. 



Make gelatin stabs of all organisms and keep at or below 

 20 C. Note the place of pigment formation. Explain. 



