4 To find out whether water is contaminated with sewage bacteria, inoculate 

 fermentation-tubes of brilliant green-bile medium^ with 1 cc of each of several 

 samples of water. Try samples from wells, springs, swimming pools, rivers and the 

 hke. Incubate the cultures at 37.5° C. Examine in 24 hours to see whether fermen- 

 tation has produced gas in any of the cultures. The presence of gas indicates the 

 presence of Bacillus coll.- Summarize results to show which of the waters are and 

 which are not safe to drink, or to swim in, 



5 To determine the relative number of bacteria present in various places, expose 

 sterile agar plates and find out how many bacteria grow from each inoculation. Ex- 

 pose dishes to the air in the classroom, in the street, in the home; test clean silver- 

 ware and dishes; expose plates to doorknobs, drinking fountains, pencils, coins, 

 fingers (both before and after careful washing with soap). Inoculate other plates by 

 kissing, by sneezing, with scrapings from under the fingernails, with combs, with 

 used handkerchiefs, with dishwater, with footprints of a housefly, etc. Incubate cul- 

 tures and examine after 24 hours. Tabulate and summarize your results, to tell in 

 what kinds of places bacteria are abundant. Relate your findings to the spread of 

 disease. 



6 To study the sanitation of your community, take trips to the water- 

 purification plant, the incinerator, and the sewage-disposal plant. Find out how each 

 operates. If such plants are not accessible for study, investigate the water supply of 

 various homes or farms, as well as methods used in disposing of refuse and sewage. 

 Report your findings. 



7 To find out about the work of your local health department, arrange to visit 

 its bureaus or divisions of statistics, foods and drugs, and preventable diseases; the 

 laboratories, and various cfinics, especially those deaUng with child health, tuber- 

 culosis and venereal diseases. Plan a panel discussion in which you share your 

 findings. 



QUESTIONS 



1 In what ways can we prevent the spread of communicable diseases.? 



2 Why are not doctors and nurses, who are so much in contact with sick 

 people, more often sick than others.? 



3 What is the advantage of having physicians report certain diseases to the 

 state or city health officer.? What is the disadvantage.? 



4 How can one preserve his own health without depending upon others.? 



^Brilliant green-bile medium can be purchased in dry form from laboratory supply houses. This 

 medium contains three ingredients which differentiate Bacillus coli from other forms of bacteria, 

 namely, anihne dye, which is poisonous to other bacteria, but not to B. coli in the dilution used; 

 bile, which kills most bacteria, but which does not inhibit the growth of B. coli; and lactose sugar, 

 which is fermented readily by B. coli but not by most other bacteria. The formation of gas in 

 this medium within a period of 24 hours is quite conclusive evidence of the presence of B. coli. 

 If gas does not form within 24 hours, but does form to a limited extent later, the test is considered 

 negative, as soil bacteria of a certain group also grow to a limited extent in this medium. 



^Bacillus coli normally grows within the intestines of warm-blooded animals. The presence of 

 B. coli in a sample of water indicates contamination with fecal matter, which may or may not be 

 human excreta. If human excreta are draining into the water, there is, of course, danger that in- 

 testinal parasites which cause typhoid fever may also be present. 



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