Germ Theory
 Acceptance
of germ theory highly
significant for medicine
 Reformation of both theory and
practice
– Immunology
– Antiseptic/aseptic surgery
– Public health
 Made
medicine more effective
Refuting Spontaneous Generation
 Bacteriology
began in 17th century
 No
one knew if bacteria had a
biological function
 Commonly
believed the putrefaction
(spoilage) generated bacteria
 Based
on older belief in spontaneous
generation
– Mice
– Maggots
 Francisco
Redi (c.1621 – c.1697)
– Proved maggots were not sponanteously
generated
 People
still assumed bacteria could
spontaneously generate
 John
Tuberville Needham (17311781)
– Apparently proved this hypothesis
– Bacteria appeared in sterilized broth



Lazzaro
Spallanzani (17291799)
Sealed flasks after
sterilizing broth
No bacteria
 Claimed
to have disproved
spontaneous generation
 Critics
claimed all it proved was that
spontaneous generation could not
occur without air
 Debate
century
not resolved until the 19th



Louis Pasteur
(1822-1895)
Disagreed with
theory of
spontaneous
generation
Strongly influenced
by his religious
beliefs
 Those
who opposed Darwin’s theory
also opposed spontaneous
generation
 Appeared
morality
 Pasteur’s
to threaten human
work in the wine industry
caused him to believe that bacteria
caused fermentation (not vice versa)
 Pasteur
was opposed by Felix
Pouchet (1800-1872)
 Demonstrated
that even carefully
sterilized infusions would spoil if
exposed to oxygen
 Declined
to enter into a public
contest with Pasteur
 In
fact, Pouchet might have won
 No
one knew about heat resistant
(spore forming) bacteria
 In
later years, Pasteur was forced to
admit that these organisms could
threaten sterilizing techniques
 Today,
scientists believe that life did
arise spontaneously on early Earth
 So,
 By
was Pasteur correct or not?
1890s, spontaneous generation
rejected as an explanation for
putrefaction
Accepting Contagion Theory
 Prior
to 19th century, contagion
theory not accepted
 Some
observed facts seemed to fly
in face of contagion
 Diseases
could break out in widely
separated areas of the country
 People
who attended the sick didn’t
always succumb to the disease
 Miasma
(bad air) a common
experience in crowded urban
environments where disease broke
out
 Also
evidence that supported
contagion theory
 Sometimes
 Outbreaks
routes
attendants did get sick
often followed trade
 Debate
divided 19th century medical
community
 Had
huge implications for disease
control
– Quarantine
– Public health policy



John Snow (18131858)
Transmission of
cholera
Traced 1854
outbreak to a
water pump on
Broad St.
 Cholera
transmissible in water
 William
Budd announced similar
conclusion days later
 Did
not know what spread the illness
 Budd
speculated that it was a fungus
 Next
step in acceptance of germ
theory was to establish that bacteria
passed from one victim to another
 Casimir-Joseph
Davaine (1812-1882)
 Studied anthrax in cattle
 Identified large microbes in blood of
infected animals



This discovery
received little
attention
Robert Koch
(1843-1910)
Intrigued by
Davaine’s findings
 Discovered
that anthrax bacteria
formed spores
 Able
to relate this finding to the
epidemiological facts surrounding
outbreaks
 Published
findings in 1876; one year
before Pasteur
 1880:
Published on bacteria found in
surgical infections
 1882:
Discovered M. tuberculosis
 1883:
Dicovered V. cholerae
 Success
based on exceptional
technical expertise
 Development of solid culture media
 .Germ
theory commonly accepted by
medical community
 1880-1900
golden age of
bacteriology
 New bacterial diseases identified at
rate of 1/yr
– Gonococcus
– Syphilis
– Child bed fever
 Fuelled
hopes that diseases such as
cancer also caused by germs
Impact of Germ Theory
 Dramatic
consequences for public
health
 Emphasis on breaking chain of
infection
– Discovery of healthy carriers
– Typhoid fever
– Story of typhoid Mary
 Germ
phobia & changes in hygienic
practices
 Decline
of the theory of
predisposition
Immunology
 Based
on the fact that living entities
have immune systems
 Can artificially produce immunity
– Artificial passive immunity
– Artificial active immunity
 Smallpox
& artificial active immunity
already discussed
Immunology After Vaccination
 Several
other vaccines were
produced in the late 19th century
 Produced
by manipulating organisms
so that they lose virulence, but
retain capacity to produce antibodies
– Attenuated vaccines
– Killed vaccines
 Pasteur
played significant role
 Accidental attenuation of chicken
cholera organism
 Discovered it rendered chickens
immune to the virulent organism
 Used
this model to develop anthrax
vaccine
 Also
developed rabies vaccine
 Pasteur
criticized by some of his
contemporaries and present day
historians
– Used unproven vaccine on Joseph
Meister
– Appropriated techniques developed by
other researchers
– Was not completely honest about how
he produced anthrax & rabies vaccine
 Stakes
were very high for these
researchers
 General public desperate for
solutions
 Koch
and development of tuberculin
another example
 Impact
of vaccines
– Mortality due to contagious diseases fell
dramatically
– Mortality shifted to chronic diseases
 Other
impacts of germ theory
– Search for specific remedies
– Abandonment of general therapies
– Reduced mortality after introduction of
aseptic techniques