Enhancing Thinking Skills in Science Context Fever Lesson 3 Testing a Hypothesis

Activity 1 Part I of Ignaz Semmelweis ’ Discovery to the cause of Childbed Fever

 Ignaz Semmelweiswas a doctor who worked in an Italian Hospital in 1840s. He noticed that many women died shortly after childbirth in the ward (first ward) he and his colleagues were working. He called this phenomenon as “ childbed fever ” ( 產褥熱 ).  He observed that the death rate due to childbed fever in the first ward was higher than that of the second ward attended only by midwifery students (Ignaz Semmelweisand other doctors did not help with the delivery of maternity patients in this ward) in the hospital for 3 consecutive years. The death rates of the maternity patients in the first and second ward of the hospital were as follows ﹕

YearDeath rate of maternity patients after child birth in the first ward Death rate of maternity patients after child birth in the second ward %2.3% %2.0% %2.7% (Reference: Carl G. Hempel(1966))

 There were some hypotheses suggested to explain the above observations.   You will be divided into groups of 4-5 students.   Each group will be required to discuss the possibility of the different hypotheses.   You are required to write down your discussion result in the form of a mind map.   You may get further information on each hypothesis from the teacher after completion of the mind map.

Hypothesis I: Atmospheric Change Hypothesis  The cause of the higher rate of childbed fever is due to atmospheric- cosmic changes ( 大氣變化 ).

Task 1:  What other information do you need to know before you agree or disagree with this hypothesis? Write down your discussion result with the aid of a mind map.   Task 2 (Your teacher will give you further information after you have completed task 1)   Can this hypothesis be used to explain Semmelweis ’ findings?   Explain your answer.

Hypothesis 2: Crowdedness Hypothesis  The cause of the higher rate of childbed fever is due to crowdedness in the first ward.

Hypothesis 3: “Rude Manner In Examination” Hypothesis  The cause of the higher rate of childbed fever in the first ward was due to the rude manner of medical students when they examined the pregnant mothers between deliveries.

Hypothesis 4: “Position In Delivery” Hypothesis  The cause of the higher rate of childbed fever in the first ward was due to the supine position (lying flat on the back, face upwards) of pregnant mothers in delivery.

Part II of Ignaz Semmelweis’ Discovery to the cause of Childbed Fever  One colleague of Semmelweis, professor Kolletschka cut his own finger with a scalpel by accident when he was performing an autopsy. Such accidents happened quite often among doctors between deliveries. Professor Kolletschka developed symptoms similar to childbed fever later and died.

Group Discussion a. If you were Semmelweis, what would you think? (any causal relationship between the accident and Professor Kolletschka ’ s death) b. Can you suggest a hypothesis to explain his death? a. What evidence was needed to support the hypothesis in (b)?

Part III of Ignaz Semmelweis’ Discovery to the Cause of Childbed Fever  Semmelweis thought that it was the cadaveric matter in the corpse that entered the blood of professor Kolletschka infecting him with childbed fever.   cadaveric matter  scalpel  blood of professor Kolletschka  childbed fever  death

Testing of his own Hypothesis:  Semmlweis then instituted a strict policy in the first ward. Semmlweis, his colleagues and medical students used chlorinated lime (bleaching powder) to wash their hands prior to attending patients.   The death rate of maternity patients dropped from 18.3% to 1.3% in 1848 and was even lower than that of the second ward (death rate: 1.33%).   We call the cadaveric matter ‘ bacteria ’ nowadays.

Activity 2: Reference: Learning from TIMSS (2006) Procedure: (a) Light up three candles of different lengths (tall, medium, short). (b) Predict the going out sequence of the candle flame when the three burning candles are covered with a bell jar as shown in the diagram below ﹕

Activity 2: (c) Cover the three burning candles with a bell jar. (d) Observe what happens and write down the results.

Activity 2:  Suggest a hypothesis to explain the above observation. Write down the steps to test your hypothesis. Then carry out the experiment if possible and see whether your hypothesis is right or wrong. If it is wrong, you need to think of a new hypothesis and test it again.

Remarks:  The flame of the tallest candle would go out first, then the medium size and finally the shortest one.  The reason is that burning of the candles would produce carbon dioxide and the heat evolved would heat up carbon dioxide that rise upwards due to smaller density.  The accumulation of a large amount of carbon dioxide at the top of the bell jar would put out the candle flame of the tallest candle first.

Activity 3  Write down the logic of testing a hypothesis (Home Assignment).

 Suggested answers:  We can test scientific hypotheses by considering their implications and then use experiments or observation to test those implications.

Type 1 Hypothesis Let H be the hypothesis and I be the implication.   If H is right, then I would happen. (If H, then I)   I is not observed. (Not I )   So H is not right. (So, not H)

Illustration of Type I Hypothesis  Hypothesis: Virus X would infect people through air transmission  Implication: People would be infected with virus X if they talk to each other.   Observation / Result: It is found that it is not the case that people became infected with virus X after talking to each other.  The observation and experiment in Type 1 Hypothesis refute the hypothesis. Deduction is widely used in scientific reasoning.

Type 2 Hypothesis  If H is right, then I would happen. (If H, then I)   I is observed. (I )   So H is right. (So, H)

Illustration of Type 2 Hypothesis  Hypothesis: If dogs urinates in the street, then the streets are wet.   Observation: The streets are wet.   Conclusion: Therefore, dogs urinated.   Remarks 1: The above argument does not prove that dogs urinated. It might be the case but might be some naughty boy did so.   Remarks 2: Type 2 pattern of reasoning affirms the consequent implication. If the observation in Type 2 Hypothesis occurs, the hypothesis will be supported. However, the arguments in type 2 are not deductively valid.

Activity 3  Scientists always put up a hypothesis, deduce implications from the hypothesis, test the implications by experiments and find out whether the experimental result confirms or refutes the hypothesis.   Due to the reason as exemplified by illustration of Type 2 Hypothesis scientists can never be 100 percent certain that a scientific hypothesis is true. Scientific conclusions are always tentative and open to revision or correction. However, scientific conclusions can be affirmed with a high degree of confidence by means of carefully controlled experiments.