In 1478 a book by the Roman doctor Celsus was printed. (The printing press made all books including medical ones much cheaper). The book by Celsus quickly became a standard textbook. However in the early 16th century a man named Theophrastus von Hohenheim (1493-1541) called himself Paracelsus (meaning beyond or surpassing Celsus). He denounced all medical teaching not based on experiment and experience. However traditional ideas on medicine held sway for long afterwards.
In 1880 Pasteur and a team of coworkers searched for a cure for chicken cholera. Pasteur and his team grew germs in a sterile broth. Pasteur told a coworker to inject chickens with the germ culture. However the man forgot and went on holiday. The germs were left exposed to the air. Finally, when he returned the man injected chickens with the broth. However they did not die. So they were injected with a fresh culture. Still they did not die.

Humans evolved to live as simple hunter-gatherers in small tribal bands. Contemporary humans now have a very different environment and way of life.[13][14] This change makes present humans vulnerable to a number of health problems, termed "diseases of civilization" and "diseases of affluence". Stone-age humans evolved to live off the land, taking advantage of the resources that were readily available to them. Evolution is slow, and the rapid change from stone-age environments and practices to the world of today is problematic because we are still adapted to stone-age circumstances that no longer apply. This misfit has serious implications for our health. "Modern environments may cause many diseases such as deficiency syndromes like scurvy and rickets".[15])
The Roman contribution to the history of medicine is often overlooked, with only Galen, of Greek origin, believed to be notable of mention. However, this does the Romans a great disservice and they put their excellent engineering skills to use in preventative medicine. The Romans understood the role of dirt and poor hygiene in spreading disease and created aqueducts to ensure that the inhabitants of a city received clean water. The Roman engineers also installed elaborate sewage systems to carry away waste. This is something that Europeans did not fully understand until the 19th Century; before this period, sewage was still discharged close to drinking water.
Herophilus of Chalcedon, working at the medical school of Alexandria placed intelligence in the brain, and connected the nervous system to motion and sensation. Herophilus also distinguished between veins and arteries, noting that the latter pulse while the former do not. He and his contemporary, Erasistratus of Chios, researched the role of veins and nerves, mapping their courses across the body. Erasistratus connected the increased complexity of the surface of the human brain compared to other animals to its superior intelligence. He sometimes employed experiments to further his research, at one time repeatedly weighing a caged bird, and noting its weight loss between feeding times. In Erasistratus' physiology, air enters the body, is then drawn by the lungs into the heart, where it is transformed into vital spirit, and is then pumped by the arteries throughout the body. Some of this vital spirit reaches the brain, where it is transformed into animal spirit, which is then distributed by the nerves.[50]
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