Popular Science Monthly/Volume 66/March 1905/Simple Bacteriology for Public Schools
|SIMPLE BACTERIOLOGY FOR PUBLIC SCHOOLS.|
By LILLIAN CHAPIN, B. S.,
INSTRUCTOR IN CALUMET HIGH SCHOOL, CHICAGO.
HYGIENE is the one secondary school subject that every pupil will find necessary throughout life. In few high schools, however, has it received the treatment a subject of such importance demands. This article is a plea for definite, forceful experiments and demonstrations in hygiene comparable with the experiments and demonstrations so long deemed essential in physics and chemistry. The following experiments could be done in any secondary school.
1. To demonstrate Bacteria in the Air.—A test-tube of sterile nutrient agar was melted by immersing it in boiling water. The agar was then poured into a sterile Petri dish, where it cooled and solidified in a thin film. The cover of the dish was then removed and the medium exposed to the air for ten minutes. The cover was replaced and the dish set aside. Two days later, there had developed on the agar 63 colonies of bacteria. A dish prepared in the same way, but not exposed to the air, developed no colonies.
2. To demonstrate Bacteria in Water.—A test-tube of agar was melted and placed in water at 42° C, a temperature slightly above that of the human body. At this temperature, agar remains liquefied, but it is not hot enough to kill bacteria. Two tiny drops of drinking water were transferred to this melted agar by means of a small, sterile loop of platinum wire. The agar was then poured into a sterile Petri dish. A few days later, the dish was found to contain fourteen colonies of bacteria.
3. To demonstrate Bacteria in Milk.—In the same way, a test-tube of agar was inoculated with two tiny drops of milk, and the agar poured into a sterile Petri dish. In this dish 192 colonies developed.
4. To show the Effect of Heat on Bacteria.—Three test-tubes of milk were taken. The first was kept at room temperature, the second was immersed in water at 60° C, and the third placed in boiling water. At the end of twenty minutes, Petri dishes were prepared from each tube, with the following results:
|Milk heated to 60° C||13||"|
|Milk heated to 100° C||5||"|
5. To determine the Effect of Freezing upon Bacteria.—Two test tubes of water were used. One was kept at room temperature, the other was frozen solid by means of a mixture of salt and ice. At the end of twenty minutes the frozen specimen was allowed to melt. Petri dishes were then prepared from each, with the following results:
In a similar experiment with milk, 192 colonies developed from the sample kept at room temperature, and 193 colonies from the sample frozen.
6. To show the Effect of Temperature on the Rate of Multiplication of Bacteria.—Three test-tubes of milk were used. A Petri dish made from the milk at this time showed 80 colonies of bacteria. The first tube was placed in an ice chest, the second was kept in a locker, and the third was put in an incubator. Petri dishes made from each, twenty-four hours later, showed the following counts:
|Ice chest (4° C.)||70||colonies.|
|Locker (20° C.)||30,000||"|
|Incubator (37° C.)||100,000||"|
7. To show the Effect of Drying on Bacteria.—Three loops full of beef broth in which typhoid fever germs were growing, were transferred to each of two dry, sterile test-tubes. Into the first tube, melted agar was poured, and then poured out into a sterile Petri dish. The drops in the second test-tube were allowed to dry, and a day or two later a Petri dish was prepared from this tube in the same way. The two Petri dishes showed the following counts:
|Specimen not dried||6,000||colonies.|
8. To determine the Effect of Sunlight on Bacteria.—Two slips of filter paper were wet with a beef-broth culture of typhoid. The papers were placed in sterile test-tubes, which were sealed with paraffine to prevent drying. One of the test-tubes was placed in a locker. The other was exposed to sunlight for three hours. Petri dishes were then prepared, which showed the following counts:
|Paper not exposed to sunlight||100,000||colonies.|
|Paper exposed to sunlight||0||"|
9. A study of Antiseptics.—Four test-tubes were prepared, each containing 5 c.c. of water to which typhoid bacilli had been added. To the first tube nothing was added. Half a cubic centimeter of a weak solution of the antiseptic to be tested was added to the second. To the third, 1 c.c., and to the fourth 2 c.c. of the antiseptic. Twenty minutes later Petri dishes were prepared from each tube, with the following results:
|Antiseptic.||0 c.c.||1⁄2c.c.||1 c.c.||2 c.c.|
|5 per cent. Carbolic Acid||446||237||95||20|
|95 per cent. Alcohol||446||96||25||1|
|Salicylic Acid (Sat. sol.)||3640||298||60||15|
|01 per cent. Mercuric Chloride||3640||3||1||0|
10. To disinfect a Room.—Three slips of filter paper were moistened with a beef-broth culture of typhoid, and placed in large glass jars. In the first jar sulphur was burned. Into the second jar formaline vapor was passed. The third jar was not treated with a disinfectant. A few hours later, Petri dishes were prepared from each paper. They showed the following counts:
11. To show the Effect of Food Preservatives on the Pate of Multiplication of Bacteria.—Two test-tubes, each containing 5 c.c. of fresh milk, were used. A Petri dish made from the milk at this time showed 83 colonies of bacteria. To one of the tubes about two grams of common salt were added. The second tube was not treated. The tubes were kept in a locker over night. Petri dishes were then made from them with the following results:
12. To show the Antiseptic Properties of Gastric Juice.—An artificial gastric juice was prepared by dissolving a little pepsin in a 1⁄4 per cent, solution of hydrochloric acid. To 1 c.c. of this juice, 1⁄4 c.c. of a beef-broth culture of typhoid bacilli was added, and Petri dishes made from the mixture at intervals for half an hour. The number of colonies developing on these dishes is tabulated below. To get an idea of the number of germs originally added to the gastric juice, the same amount of typhoid culture was added to 1 c.c. of sterile water and a Petri dish prepared from this mixture. The number of colonies on this dish is recorded as the count for minutes.
13. To show the Antiseptic Properties of Human Serum.—Under the supervision of a physician, a small amount of blood was drawn, by means of a hypodermic needle, from a vein in the arm. This blood was placed in a sterile glass vessel and allowed to clot. After standing some time, serum separated. One cubic centimeter of this serum was placed in a small test-tube and five loops full of a beef-broth culture of typhoid bacilli were added to it. Petri dishes were made from this mixture at intervals for an hour. To get an idea of the number of germs originally placed in the serum, a control was run with 1 c.c. of sterile water. The count made from this control is recorded as the count for 0minutes.
12. To show that Bacteria are not given off from a Moist Surface.—A culture of harmless, brilliant yellow bacteria was smeared on the inside of a large glass tube. Through this tube a strong current of air was directed on to agar in a Petri dish. If bacteria were given off into the air from the moist surface, they would be blown upon the agar, where they would develop into colonies. The Petri dish used in this experiment developed no yellow colonies. The smear was now allowed to dry and was then crushed with a sterile glass rod. A second current of air was now directed through the tube into another Petri dish. This dish developed 240 colonies of yellow bacteria.
The above is merely suggestive of the kind of work that might be done in any secondary school. Most of these experiments could be performed by the average high school senior. All of them could be used as class demonstrations. Each one has a direct bearing on some large question of preventive medicine. A week's training in bacteriological technic will enable any teacher to give this work.
The experiments here outlined were suggested to me by Dr. W. H. Manwaring, and were carried out in the Pathological Laboratory of the University of Chicago, during the summer of 1904.
- In repeating this experiment in high schools, harmless bacteria must, of course, be used. The colon bacillus is recommended for this purpose.