Name:____________________________________________Date: _______

Early Discoveries in Science  -   CER Practice

For each short story, identify the CLAIM by highlighting green.    Find any EVIDENCE statements and highlight in yellow.  Complete the sentence to illustrate how REASONING was used in the scientific discoveries.

meat in jar1)  In 1668, Francesco Redi wanted to know if meat could spontaneously produce maggots as many people thought at the time.  Redi believed that the maggots came from flies that lay eggs on the rotting meat.  He placed one piece of meat in a jar and covered it with cloth.  He left another piece of meat in a jar uncovered.   After two weeks, he inspected the meat and found that the one in the covered jar did not have maggots, but the one open to the air did have maggots.

REASONING:      If maggots were spontaneously being produced by the meat, then ….



map2)  In 1554, a cholera outbreak occurred in London.  Cholera is a disease that causes intense diarrhea and can be fatal.   At the time, many people believed that diseases were caused by “bad air.”    John Snow had another idea; he thought that cholera was caused by something in the environment where people lived.   He went door to door and made a map showing households that had cholera.  He found that most of the cases were near the Broad Street Water Pump.    John Snow made a case that the water from the pump was making people sick and the pump was shut down.

REASONING:   If water was the cause of the sickness, then …


s-shaped flask3)  Louis Pasteur felt that liquid would spoil because there were particles in the air that could enter the liquid and grow there.    He boiled liquid broth and then placed it in flask that had an S-shaped neck.   Air could enter the neck of the flask, but any particles would be trapped in the neck.   After a week, the liquid was still clear, showing that no growth occurred.    Pasteur then broke the neck from the flask and let it sit for another week.  This time, he saw that the broth became cloudy and spoiled.   Louis Pasteur’s experiments lead to a process that could keep food fresh for longer, a process called “pasteurization.”

REASONING:    If particles in the air could cause food to spoil, then



bacteria4)  A hospital in Vienna noted that many of their female patients were dying of “childbed fever” after they had given birth in the hospital.  The rates of this fever were much higher in the hospital than they were for women who had given birth at a different clinic.   In fact, 10% of the women at the hospital contracted fever compared to 4% at the clinic. 

Ignatz Semmelweis was a doctor at the clinic and he felt that the fever was being transmitted on the hands of doctors when they went from the morgue to examine women.    He asked the doctors to wash their hands and the number of cases of “childbed fever” were reduced.    He also noted that a doctor contracted the same fever after he cut himself with a scalpel that had been used on an autopsy.    

Semmelweis concluded that the fever was caused by some element that could be transferred from person to person.

REASONING:    If fever as something that could be transferred from person to person, then …


penicillin sign5)   Alexander Fleming was working with a bacteria called staphylococcus, which looked like bunches of grapes under the microscope.  He could grow colonies of these bacteria on petri dishes with a growth medium.   When he returned from vacation, he found that several of these dishes had become contaminated with a fungus.  The colonies near where the fungus was growing had been destroyed.   Fleming then grew the mold and purposefully added it to a petri dish that contained bacteria colonies.   The colonies exposed to the mold died.   Fleming named the substance within the mold that killed bacteria “penicillin.” 

REASONING:   If mold contains a substance that kills bacteria, then …


sheep6) For many years, scientists believed in the “Miasma Theory” which suggested that many diseases, such as cholera and the black death, were caused by pollution or bad air.   Hospitals would air rooms out daily by opening windows to remove any bad air that might infect patients.    When microscopes were invented, scientists could view very tiny organisms that lived in water and on surfaces all around them.   Many scientists believed it was these “germs” that spread disease and not the air.   

Robert Koch was able to isolate microorganisms from sheep that had contracted anthrax.  He grew these bacteria and then injected them in mice.  The mice became sick with anthrax.

REASONING:   If microbes (germs) were responsible for causing anthrax, then...



*These experiments lead to the development of the GERM THEORY and the modern discipline of EPIDEMIOLOGY*