Van Helmont’s Recipe for Mice

• Place dirty rags in an open pot or barrel

containing grains of wheat or some wheat

bran.

• In 21 days mice will appear.

• There will be adult males and females

present. They will be capable of mating

and reproducing more mice.

Recipe for Bees

• Kill a young bull.

• Bury it in an upright position so that its

horns protude from the ground.

• After a month, a swarm of bees will fly out

of the corpse.

CHARACTERISTICS OF LIFE

I)Spontaneous Generation A) living things can arise from non-living

things

1) stated by Aristotle (325 BC)

a) frogs from mud

People believed this for about 2000 years!!!

Spontaneous Generation

• Until the 1600s most people accepted the

idea that living things (animals) could

spring from non-living materials

• What eventually happened to Spont.

Gene. Is a great example of hypotheses

can be tested and retested and changed

to reflect new evidence

b) rats from sewage

2) Van Helmont’s mice

Someone named Redi

attempted • 1660s Redi challenged the idea of Spon.

Gen

• He was curious about how maggots

appeared on decaying meat

• Much like how mold can form on a loaf of

bread…how does it get there?

B) disproving the theory

1) Redi (1668)

a) maggot experiment

i) so well designed!

- # samples

- use of controls

- different seasons

- observation

Where do microorganisms come

from? • Pond water, rain water, scrapings from

your teeth, etc…all these contain

microorganisms

• Sketches and drawings are popular

methods for explaining what people

observe under a microscope. You will be

sketching OFTEN!

2) step backward with Leeuwenhoek

a) use of microscope

b) new support for spontaneous generation

i)“animalcules”

Spontaneous Generation

again… • Leeuwenhoek’s discoveries helped feed

proof of Spontaneous Generation

• Large numbers and rapid appearance of

these tiny living things were hard to

explain

• Broths were normally examined, once they

turned cloudy they had a large presence of

mircoorganisms

• Observes concluded they must have come

from nonliving organisms

How would you go about killing

microorganisms? • Some scientists decided to ensure that the

broth had no microorganisms to begin

with…

• How do you think they went about this?

• Why?

3) Needham’s meat broth (1748)

a) 5-10 min boiling with sealed cork

i) microorganisms appear though

4) Spallanzani’s experiment (1767)

a) broth boiled for 1 hour

b) melted glass seal

c) heated air = destruction of active principle

i)spontaneous generation still believed

5) Pasteur (1861)

a) finally disproves spontaneous gen.

b) “S”–shaped flask trap microorganisms but allow air through

c) flasks clear since 1861!!!!

C) Theory of Biogenesis arises

1) Huxley (1870)

2) living things come only from other living things of the same type