The sense of smell is even harder to discuss than any of the preceding senses. We humans can detect odors clearly but it may be hard to find words to describe what we are smelling. We often have to resort to saying that a certain odor smells “like something else”. We do have a surprisingly good memory for smells though. A whiff of rotting seaweed can bring back hidden memories of a childhood summer at the ocean.
WRITING ASSIGNMENT: Describe the following things by smells alone: springtime, a dentist’s office, your kitchen at suppertime. Name a smell that brings back a definite childhood memory for you. What is the memory? Is it easy or hard to describe smells by words?
Odor is a chemical sense in contrast to the preceding physical senses. In order to smell a substance it must be volatile (ammonia ). The molecules enter the nose as we breathe and dissolve in the two olfactory organs high up in the nasal passages. The chemical sense is changed to an electric impulse which is sent via olfactory nerves to a very primitive part of the brain(which also has to do with sex and emotions).
We humans do not depend on our sense of smell for survival usually (unless the gas is on), but lower animals often do. Whereas the two olfactory patches in our nose are an inch square with about 5 million sensory cells, in a dog they are the size of a small handkerchief with hundreds of millions of cells. The olfactory region of a dog’s brain is also much larger than in humans. We know that smell plays a large role in the life of a dog when a female dog comes into heat and attracts males from miles around.
The animal that has the most developed sense of smell is probably the moth. In this year of the gypsy moth we have seen males coming from all over to mate with the flightless females clinging everywhere. The female releases a sex attractant from her abdomen which drifts downwind. Any male in the right area, up to half a mile away, can detect minute amounts of this substance with his large antennae and immediately starts flying upwind.
It has been estimated that the sex attractant is so potent that one female could theoretically attract more than one billion males. The USDA has worked for 30 years to isolate the attractant. They finally succeeded and were also able to synthesize it, resulting in the gypsy moth sex lure traps sold everywhere.
At this point assign your students LESSON 2:
Writing Science Fiction—Perception on Imaginary Planets
(at the end of the unit).
They will also be able to do LESSON 3:
Crossword Puzzle on the Senses
which is a review of the whole unit.
Experiment on Extrasensory Perception (ESP)
Are there other senses that we are not aware of, such as ESP—the ability to read another person’s mind? Many teenagers (and adults) are convinced that psychic phenomena are real and surprisingly, a substantial percentage of scientists in a recent poll felt that the existence of ESP was a “likely possibility”.
To the teacher
: The object of this experiment in ESP is not to convince students one way or the other of the existence of mental telepathy but rather to have them think about the design of the experiment and what conclusions they can validly draw from it. By repeating the experiment and making a bar graph they should see the role that probability plays. (It would be fascinating if you
have a student with consistently high results).
This experiment is based on the classic one by Dr. J. Rhine at Duke University who studied ESP for many years. Students (who work in pairs) will make their own cards with special patterns. (See Diagram 5 at the end of this unit for the patterns). A total of 25 cards are made, 5 of each pattern. One student will be the tester and the other student will “read her mind” to guess the correct pattern. They then reverse roles and the results are tallied in a class bar graph.
To the students : (work in teams of two)
Do you think it is possible to read someone else’s mind? This ability is called Extrasensory Perception (ESP). Most scientists are doubtful about ESP. See what you think after you have tried the following experiment.
1. Your teacher will show you how to make 25 cards using 5 different patterns. Shuffle them well.
2. Partners sit facing each other. The tester holds the cards so that the subject cannot see them, and turns them over one by one, concentrating hard on each one.
3. The subject (who can’t see the cards) guesses what the pattern is on each one. The tester marks down right and wrong answers.
4. Count up the correct answers. Since there is a one in five chance of making a correct guess, an average score will be about five correct.
5. How did you do? Did you guess more than 5 correctly? Switch roles with your partner and repeat the experiment after reshuffling.
6. Using the results of the whole class make a bar graph of correct answers.
7. Did anyone have a very high score? Do you think it means that she has ESP? Should the experiment be repeated?