One problem with the old theories of disease was that people believed that living things were spontaneously generated. Spontaneous generation is when something like a fly grows from a small speck of smelly meat. That old theory is called abiogenesis. In the seventeenth century, Francesco Redi (February 18, 1626 – March 1, 1697) discovered that flies lay eggs that become maggots. Prior to this, people thought that maggots came from rotting meat. He discovered this by sealing some meat in a jar and watching it. No maggots were found on the sealed meat. He also put some meat in a jar and covered it with gauze. Maggots were found on the gauze but not inside the jar. But when he placed meat in an open jar, maggots were found on the meat and inside the jar. Experiments like this proved that maggots come from flies who lay eggs, not from rotting meat. Later scientists would prove that diseases did not come from the air. Diseases are spread by infection.
Also in the eighteenth century, Antonie van Leeuwenhoek discovered the first microscopic organisms with a microscope. He was the first microbiologist. He saw some of the microscopic organisms that cause diseases, but he didn't know what they were. In 1700, Nicolas Andry thought that some of these microscopic organisms caused smallpox and other diseases. Over 100 years later, Agostino Bassi figured out what caused disease in silkworms. Ignaz Semmelweis was a doctor who figured out that if doctors washed their hands after touching dead people, that other patients wouldn't get sick. That was in 1847. It was about this time that sanitation and hand washing became popular with some, but not all doctors. Doctors began to use chemicals to cleanse wounds and clean their tools between each patient.
One of the most famous experiments of the nineteenth century was when John Snow discovered the source of a cholera outbreak. It turns out that cholera is transmitted when human waste contaminates water that people drink. Snow found out that there was a large number of sick people in Soho in London. After talking to many people in the area and mapping where each sick person lived, he realized that the sick people were almost all getting their drinking water from the same public water pump. He solved the epidemic by having the water pump's handle removed so that the people would get water from some other place. It worked, and the epidemic was soon over.
Louis Pasteur showed that the germ theory of disease was true. In 1862, he invented a process that heats up a liquid to a high temperature to keep it from spoiling. This process is known as pasteurization, named after Pasteur. Pasteurization is used to kill microscopic organisms in liquids like milk, wine, and beer. Liquids that are pasteurized will last much longer before they spoil.
Later, he did an experiment with fermentation. In one case he made a broth that he put inside a jar with a very long winding tube, so that no particles could pass to it from outside. Air could get inside the tube, but almost no dust. The broth he made did not change, and no fermentation took place.
He then took a similar broth, but this time he allowed air and dust to go inside the jar. This time, fermentation took place. The thing that caused fermentation therefore needed to come from outside (the environment). And it wasn't just air that caused fermentation, it must be something floating in the air which was very small. We now know that small particles called yeast cause fermentation.
In the latter part of the nineteenth century, Robert Koch and Joseph Lister would go on and help establish the germ theory of disease as an important part of science and medicine. Koch's theories are called "postulates" and helped medical researchers know what causes diseases. Lister's ideas would help establish sanitation as a major defense against disease. Koch's postulates and Lister's sanitation discoveries are still very important today.
We now know that small things cause diseases. Each one of these things can cause infection: fungus, bacteria, virus, prion, yeast, protist.
Labor Day
Labor Day is a holiday in the United States and Canada on the first Monday of September. This holiday honors workers. It is similar to the May Day holiday in other countries. Many businesses close on Labor Day. Many students start school the day after Labor Day.
In some countries, it is known as International Workers' Day. It is celebrated every year on May 1 in almost 80 countries in the world. The day is celebrated on a different day, such as the first Monday of September in the United States.
Christian cross
The Christian cross is the main symbol of the Christian religion. These crosses are usually found on Christian churches.
Jesus, who many Christians believe is God the Son and their Messiah, was crucified (nailed to a large wooden cross). This was a commonly used method for killing people in Roman times.
Christians believe that Jesus' death made the sins of all humans who trust in him, go away, and that they are forgiven. They also believe that Jesus was resurrected (came back to life) after three days. Because of this, the cross is a symbol for Jesus' sacrifice and suffering, but also a symbol of hope, forgiveness of sins, and victory over death.
There are several different Christian crosses that are symbols for different Christian groups or persons.
A cross with the body of Jesus on it is called a Crucifix.
The empty cross is usually favoured by Protestants and Eastern Orthodox, and the symbol reminds them of the Resurrection of Jesus, though the Orthodox will add a slanted footbar, as well. The crucifix is favoured by Catholic churches and is a reminder of Christ's sacrifice. Jehovah's Witnesses believe that Jesus died on a simple upright pole, a "torture stake" ; and only display it as a picture of an impaled Jesus in their literature.
Christians remember the death of Jesus on the cross on Good Friday every year.
The most common cross is the Latin Cross. The cross represents and memorializes Christ's death.
This cross is a symbol of hope over death, and of victory in returning to life. (See Philippians 2:8-9)
Martin Luther King, Jr. Day
Martin Luther King, Jr. Day is a US Federal Holiday. It commemorates civil rights activist Martin Luther King, Jr.'s birthday. It is celebrated on the third Monday in January and is one of only four United States Federal holidays to honor an individual person.
President Ronald Reagan signed a bill, proposed by Representative Katie Hall of Indiana, to create a federal holiday honoring King. The holiday was observed for the first time on January 20, 1986. It is observed on the third Monday of January.
Washington's Birthday
Presidents' Day, originally was two separate observances, Abraham Lincoln's birthday, which was February 12, and George Washington's birthday, which was February 22. The two observances were combined in 1971 into a single observance which is held on the third Monday in February.
Memorial Day
Memorial Day is a national holiday in the United States. It is also a state holiday in many states. The holiday honors troops who have died in past wars like World War I and the Korean War. Memorial Day was first held in 1865 after the American Civil War. It was called Decoration Day at that time. The holiday was first called Memorial Day in 1882, and became a federal holiday in 1967. On June 28, 1968, the United States Congress made a law that said that the official Memorial Day holiday is May 30, but that Memorial Day was to be observed by Federal Employees as a paid holiday on the last Monday in May. Memorial Day is thought of by many Americans as being the start of summer. It was founded by John A. Logan(General).He fought in the Civil and Mexican–American War.
Columbus Day