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Multiple experimental evidences have confirmed that at the molecular level, cancer is caused by lesions in cellular DNA.
Acute bronchitis is an inflammation of the breathing tubes (bronchi), which causes increased mucus production and other changes. It is usually caused by bacteria or viruses, can be serious in people who have pulmonary or cardiac diseases, and can lead to pneumonia.
For about 100 years, scientists thought that peptic ulcers were caused by stress, spicy food, and alcohol. Later, researchers added stomach acid to the list of causes and began treating ulcers with antacids. Now it is known that peptic ulcers are predominantly caused by Helicobacter pylori, a spiral-shaped bacterium that normally exist in the stomach.
In 1844, Charles Goodyear obtained the first patent for a rubber condom.
As the western states of America were settled, pioneers often had to drink rancid water from ponds and other sources. This often resulted in chronic diarrhea, causing many cases of dehydration and death that could have been avoided if clean water had been available.
![These two species of bedstraw grow predominately on different soil types: Galium saxatile (shown her](https://biology-forums.com/gallery/47/medium_33_17_02_12_5_28_58_1945647.jpeg)
![Multiple-dose drug administration: drug A and drug B are administered every 12 hours; drug B reaches](https://biology-forums.com/gallery/47/medium_46687_12_12_14_7_07_22_19567430.jpeg)