46 STUDIES IN MICROBIOLOGY (3) 



Exercise VIII 



Examine the different growths under the low 

 power of the microscope. (You may place the 

 petri dish right on the stage.) Record your 

 observations. 



Mold colonies are quite beautiful under low 

 power. It should be possible to see numerous 

 strands, or mycelia, which weave into the agar, 

 as well as delicate stalks which lift high black 

 sacs of spores. (Note: If there are sporulating 

 molds on the plate, please refrain from agitating 

 them, lest the spores spread into the room and 

 contaminate the blood agar plates.) 



Make wet mounts of some of the bacteria 

 and examine them under the high power of your 

 microscope. Can you see cells? What shapes 

 do they have? Are they motile? Record any 

 other interesting observations. 



N. H. Horowitz, "The Gene,"' Sci. Am. 195, No. 

 4, 78-90, Oct. 1956, Reprint No. 17. 



R. Y. Stanier, M. Doudoroff, and E. A. Adel- 

 BERG, The Microbial World, Prentice-Hall, 1957, 

 pp. 393^01. 



On genetic transformation: 



E. L. WooLMAN and F. Jacob, "Sexuality in 

 Bacteria," Sr/. Am. 195, No. 1, 109-118, July 1956, 

 Reprint No. 50. 



R. Y. Stanier, et al.. op. dr., pp. 393-401. 



K. V. Thimann, Life of Bacteria, Macmillan, 1955, 

 pp. 575-576. 



On culture conditions: 



R. Y. Stanier, er al., op. cit., pp. 42^5; 48^9. 

 K. V. Thimann, op. cit., pp. 132-154. 



Further reading 



On the nature of the genetic material: 



A. E. MiRSKY, "The Chemistry of Heredity," Sci. 

 Am. 188, No. 2, 47-57, Feb. 1953, Reprint No. 28. 



F. H. C. Crick, "Nucleic Acids," Sci. Am. 197, 

 No. 3. pp. 188-200 Sept. 1957, Reprint No. 54. 



On the ecology of microorganisms and diseases: 



R. Y. Stanier, et al., op. cit., pp. 417-573. 



On antibiotics: 



R. Y. Stanier, et al., op. cit., pp. 257-258. 

 K. V. Thimann, op. cit.. pp. 682-685. 



EQUIPMENT 



Per student 



5-ml pipet, sterile 



2 dropper pipets, sterile 



wide tube, sterile 



2 small tubes, sterile 



6 small tubes containing 0.85% sodium chloride 

 solution, sterile 



blood agar plate with streptomycin 



glass rod 



bacteriological loop 



bunsen burner 



compound microscope 



slide and cover slip 



agar plate containing synthetic medium 



nutrient agar plate (half with penicillin, half with 



streptomycin; 1000 units/ml is a convenient concen- 

 tration of each) 



Per 8 students 



cultures of cells of streptomycin-resistant Piieiimo- 



coccus (45 ml) 



cultures of cells of streptomycin-sensitive Pneumo- 



cocciis, competent for transformation, in small tube 



immersed in beaker of ice (3 ml) 



Pneiimococcus medium with glucose added, in wide 



tube (20 ml) 



dropping bottle of 5% deoxycholic acid, neutralized 



alcohol, in reagent bottle (100 ml) 



Per 30 students 



3 or 4 water baths at 37°C 



1 water bath at 30°C 



bin for incubating agar plates 



