Biology: Discoveries in Microscopy

Study Notes

First to discover cells
Used a compound microscope to study the bark of a cork tree
Observed empty cell walls of dead plant tissue
Called the pores "cells" because they reminded him of the cells inhabited by monks living in a monastery

Published extensive, accurate observations of microorganisms
Constructed simple microscopes with double convex glass lenses
Microscopes could magnify around 50 to 300 times
Observed a variety of things like rainwater, pond water, and scrapings from his own teeth
Saw minute moving objects and called them “animalcules”
First to record microscopic observations of muscle fibers, blood cells, algae, etc.

Belief that living organisms could develop from non-living matter
Challenged by Francesco Redi who conducted experiments on decaying meat and its ability to produce maggots
The discovery of microorganisms renewed the controversy
John Needham argued that boiled extracts of hay or meat gave rise to microorganisms after a while, even though larger organisms did not
Lazzaro Spallanzani improved on Needham's experiments by sealing glass flasks containing broth
Spallanzani found that if the flasks were sealed and placed in boiling water for 45 minutes, no growth took place
He proposed that air carried germs to the culture medium
Theodore Schwann allowed air to enter a flask containing a sterile nutrient solution after the air had passed through a red-hot tube. The flask remained sterile
Georg Friedrich Schroder and Theodor von Dusch allowed air to enter a flask of heat-sterilized medium after it had passed through sterile cotton wool. No growth occurred

Proved the theory of biogenesis
Discovered that yeast (unicellular fungus) was responsible for alcohol fermentation
Concluded that fermentation is caused by microorganisms
Solved the problem of wine and beer souring by heating wine to only about 50–60 °C for a short time to kill the microbes
This process is known as "pasteurization"
Proposed the “Germ theory of disease” which states that microorganisms are responsible for diseases

Provided the first direct demonstration of the role of bacteria in causing disease
Used Koch’s postulates to establish the relationship between a causative agent and its disease
His postulates are:
- The microorganism must be present in every case of the disease but absent from healthy organisms
- The suspected microorganisms must be isolated and grown in a pure culture
- The same disease must result when the isolated microorganism is inoculated into a healthy host
- The same microorganism must be isolated again from the diseased host
Discovered that anthrax was caused by a rod-shaped bacterium, Mycobacterium tuberculosis
Also discovered that cholera is caused by Vibrio cholerae
Developed more reliable and reproducible growth media employing liquid nutrient solutions solidified with gelatin, and later with agar
With Walther Hesse, Koch discovered that colonies developed on solid surfaces
Koch reasoned that each colony harbored a population of identical cells, that is, a pure culture

Discovered the existence of heat-resistant bacterial endospores
Experimenting with sterile infusions from dried hay, Cohn concluded that microorganisms might exist in thermostable forms (spores) which become active when proper nutrients are available

Developed a method to destroy microorganisms in the operating theater by spraying a mist of carbolic acid (phenol) into the air
Applied dressings soaked in carbolic acid on wounds
Successfully prevented postoperative sepsis by introducing antiseptic techniques