In the ancient times people believed that diseases were caused by some Supernatural powers. They thought these diseases were sent by the God as a form of punishment for their sins. Some thought, evil spirits enter the body and cause infections. Some attributed the Astrological phenomenon to these diseases.
Accordingly people used to treat these diseases by praying to God and perform Witchcrafts to tame the evil powers. The greek physician Hippocrates the father of medicine ignored these beliefs.
He observed the people suffering from diseases and studied how the health was influenced by diet and the environment. Through his studies he believed in the Humoral theory. Humor, refers to body fluids. The theory states that the human body consists of four body fluids.
These fluids include Blood, Phlegm, Yellow bile and Black bile. The Humoral theory states that when the four Humors are in perfect balance the body remains healthy.
Similarly, improper balance of these Humors will result in some pain. Therefore for any individual to be healthy, all these four humors must be in perfect balance.
Any deficiency or excess release of these liquids will cause disease.
Hippocrates established the Humoral theory of medicine which was focused on balancing the Humors. The cause of these Humoral imbalances was attributed to the bad air. If a person is sick, the Physician’s job was to bring back the balance of these liquids.
There were multiple ways to restore the Humoral imbalance such as, inducing vomiting, making incision and bloodletting, enema and changing the diet plans etc. However the diagnosis of the disease was based on this chart. 
This chart helped them understand what kind of treatment to provide. As shown in this chart, these four Humors are associated with four different seasons, organs, temperaments and elements of nature.
After several years, Galen’s medical investigations further supported the Humoral theory. Because of his interest in Human Anatomy he observed the bodies of people who died of diseases.
As the Roman Law had prohibited the human dissection, he performed dissections on living monkeys and pigs. From the ancient Greek times the bad air was thought to be the cause of diseases like Cholera and Malaria. This bad air was called as Miasma.
The bad air was considered to be poisonous and it could be identified by its foul or rotten smell. In 1348, when the Plague arrived at Catalonia, a Spanish physician called Jacme d’Agramount educated the general public on the preventive measures to be taken against the disease. One of his statements to the public was to shut the windows to avoid the exposure to the air.
Considering the effects of bad air, the British Parliament passed a Law in 1388, that said, deposition of dung, garbage and killed animals into the surrounding waters is prohibited. The Miasma theory was accepted by the Medical World for many centuries, as the disease spread was more rapid where there is lot of foul smell.
Therefore, all the preventive measures were based on restricting the bad smell into the public places. The real challenge was faced when the Cholera outbroke in London in 1849. As the London city was becoming more populous, the Thames river was polluted with the sewage water. William Farr, a British Government servant, stated in his report that Cholera was caused by polluted air, and geographical elevation of the city was the major cause for the spread of the disease.
However, the improved sanitary systems against Miasma theory could not completely stop the disease spread. During this period, John Snow, a British Physician, studied the causes of Cholera and came up with an idea that contaminated water was the source of Cholera, not the polluted air. Snow’s logical explanation of Cholera spread by water, could not convince William Farr, who was the leading Board member of General Health Committee in 1854.
Being the strong believer of Miasma theory, William Farr was not in a position to accept the other mode of disease transmission. Later, the continuous spread of Cholera made the scientists, including William Farr to re-look into Snow’s investigation. The final investigation concluded that contaminated water supply was the cause for the Cholera spread. William Farr finally accepted the John Snow’s explanation in 1866, by the time snow was not alive. The Miasma theory was gradually forgotten, and the Germ theory was brought into light.
