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Patients who have undergone chemotherapy for the treatment of cancer often complain of a lack of mental focus; memory loss; and a general diminution in abilities such as multitasking, attention span, and general mental agility.
Multiple experimental evidences have confirmed that at the molecular level, cancer is caused by lesions in cellular DNA.
Patients who cannot swallow may receive nutrition via a parenteral route—usually, a catheter is inserted through the chest into a large vein going into the heart.
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.
There are over 65,000 known species of protozoa. About 10,000 species are parasitic.