Work of Koch & Jenner

Koch made some observations on the disease caused Bacillus anthracci called

anthrax.Based on his findings, Koch developed the Germ Theory. The Germ Theory

states that a disease-causing microorganisms should be present in animals infected by the

disease and not in healthy animals. The microorganisms can be cultivated away from the

animal and used to inoculate a healthy animal. The healthy animal should then come

down with the disease. Samples of a microorganism taken from several infected animals

are the same as the original microorganism from the first infected animals.

Four steps used by Koch to study microorganisms are referred to as Koch’s Postulates.

Koch’s Possulates state:

1. The microorganism must be present in the diseased animals and not presence in

the healthy animal.

2. Cultivate the microorganism away from the animal in a pure culture.

3. Symptoms of the disease should appear in the healthy animal after the healthy

animal is inoculated with the culture of the microorganisms.

4. Isolate the microorganism from the newly infected animal and culture it in the

laboratory. The new culture should be the same as the microorganism that was

cultivated from the original diseased animal.

Koch ‘s work with anthrax also developed techniques for growing a culture of

microorganisms. He eventually used a gelatin surface to cultivate microorganisms.

Gelatin inhibited the movement of microorganisms. As microorganisms reproduced,

they remained together, forming a colony that made them visible without a microscope.

The reproduction of microorganisms is called colonizing. The gelatin was replaced with

agar that is derived from seaweed and still used today. Richard Petri improved on Koch’s

cultivating technique by placing the agar in a specially designed disk that was later called

the Petri dish which is still used today.

Vaccination

The Variola virus was once of the most feared villains in the late 1700s. The variola

virus causes smallpox. If variola didn’t kill you, it caused pus-filled blisters that left deep

scars that pitted nearly every part of your body. Cows were also susceptible to a

variation of variola called cowpox. Milkmaids who tended to infected cows contracted

cowpox and exhibited immunity to the smallpox virus.

i. Edward Jenner

Edward Jenner, an English physician, discovered something very interesting about both

smallpox and cowpox in 1796. Those who survived smallpox never contracted smallpox

again, even when they wee later exposed to someone who was infected with smallpox.

Milkmaids who contracted cowpox never caught smallpox even though they were

exposed to smallpox.

Jenner had an idea. He took scrapings from a cowpox blister found on a milkmaid and,

using a needle scratched the scrapping into the arm of James Phipps, an 8-year-old.

Phipps became slightly ill when the scratch turned bumpy. Phipps recovered and was

then exposed to smallpox. He did not contract smallpox because his immune system

developed antibodies that could fight off variola.

Jenner’s experiment discovered how to use our body’s own defense mechanism to

prevent disease by inoculating a healthy persons with a tiny amount of the diseasecausing

microorganism. Janner called this a vaccination, which is an extension of the

Latin word vacca (cow). The person who received the vaccination became immune to

the disease-causing microorganism.