Biology Chapter on Spontaneous Generation

Spontaneous Generation

• Early idea: Life arises from non-living matter
• Belief that life magically appears
• Examples: Meat produces maggots, mud produces fish (like mudskippers), grain produces mice

Germ Theory of Disease

• Microorganisms can invade organisms and cause disease
• Many diseases are caused by microbes, not sins, bad character, or poverty
• Belief that living things arise from nonliving components
• Examples: Maggots in rotting meat, microorganisms in cloudy broth

Spontaneous Generation Observations

• Greek philosopher Aristotle (384-322 BC) articulated the theory
• This theory persisted into the 17th century
• Life arose from non-living matter if the material contained pneuma ("vital heat")
• Dust creates fleas
• Maggots arise from rotting meat
• Bread or wheat in a dark corner produces mice

Key Experiments That Disproved Spontaneous Generation

Francesco Redi (1668)

• Italian physician
• Experiment with flies, wide-mouth jars, and meat
• Demonstrated that maggots don't spontaneously arise from meat but instead from fly eggs

Redi's Findings

• Jars with lids had no maggots.
• Open jars had maggots.
• Jars with gauze had few maggots on the gauze, but none on the meat

Lazzaro Spallanzani (1765)

• Boiled soups, sealed containers
• The soups remained clear.
• Breaking seals caused soups to become cloudy with microbes
• Critics said lack of air prevented growth

Louis Pasteur (1822-1895)

• Hypothesis: Microbes come from cells of organisms; not the air
• Put broth into special S-shaped flasks
• Boiled and placed flasks at different locations
• Microbes only appeared in flasks where organisms from the air entered

Pasteur's Experimental Results

• Boiled meat broth in a long-necked flask
• The flasks remained free of growth for an extended period
• When the flasks were turned so that particles could fall into the broth, the broth became clouded

Golden Age of Microbiology (1857-1914)

• Beginning with Pasteur's work, discoveries included the relationship between microbes and disease
• Also included immunity and antimicrobial medicine
• Germ Theory of Disease: Specific microbes cause specific diseases

Pasteur and the Germ Theory of Disease

• Pasteur showed that microbes are responsible for fermentation
• Microbial growth is responsible for spoilage of food
• Pasteur demonstrated that spoilage bacteria could be killed with heat ("Pasteurization")
• Discovered that weak forms of disease could be used as an immunization against stronger ones
• Developed vaccines for anthrax and rabies

Robert Koch (1843-1910)

• Provided proof that bacteria cause anthrax and offered experimental steps (Koch's postulates)
• Proved that specific microbes cause specific diseases.

Koch's Postulates

• The causative agent should be found in every case of the disease.
• The disease organism must be isolated in pure culture.
• Inoculation of the agent into a healthy, susceptible animal should produce the same disease.
• The disease agent should be recoverable from the inoculated, diseased animal.

Exceptions to Koch's Postulates

• Many healthy people carry pathogens but don't show symptoms.
• Some microbes are hard/impossible to grow in a lab.
• Microbes are species-specific
• Some diseases only appear when an opportunistic pathogen invades a compromised immune system

Germ Theory Summary

• Specific microbes are the cause of specific diseases.
• Developed, proved, and popularized in Europe and North America between 1850 and 1920.
• Revolutionized medicine and disease understanding.

People Who Contributed to the Germ Theory of Disease

Robert Hooke

• Believed good science resulted from observations
• Wrote Micrographia (1665)
• One of the best microscope makers of his time
• Viewed cork and observed "cells"

Anton van Leeuwenhoek

• Skillful microscope builder
• Magnified objects over 200 times
• Observed "animalcules" (microbes) in pond water
• First person to observe and record microbes

Matthias Jakob Schleiden

• Professor of Botany
• Used microscopes to study plants
• In 1838 suggested that all plants are made of cells

Theodor Schwann

• German biology professor
• Studied animals, particularly the digestive system
• In 1839 suggested that animals are made of cells

Karl Theodor Ernst von Siebold

• In 1845 suggested that microbes were made up of cells
• Mistakenly believed that multicellular organisms were made from single-celled microbes

Ignaz Philipp Semmelweis

• Hungarian doctor
• Tried to prevent childbed fever in Austria
• Concluded that childbed fever was infectious
• Felt that handwashing reduced the risk of infectious diseases

Florence Nightingale

• English nurse
• Recognized importance of cleanliness and recommended sanitary practices
• Improved conditions in military hospitals, reduced soldiers' deaths from infectious diseases

Joseph Lister

• Scottish surgeon
• Concerned about high death rates after surgery
• Idea of using chemicals to kill germs, which led to antiseptic surgery

William Stewart Halsted

• American surgeon
• Recommended using rubber gloves during surgery to prevent the spread of microbes.