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Not getting enough sleep can greatly weaken the immune system. Lack of sleep makes you more likely to catch a cold, or more difficult to fight off an infection.
Complications of influenza include: bacterial pneumonia, ear and sinus infections, dehydration, and worsening of chronic conditions such as asthma, congestive heart failure, or diabetes.
Only one in 10 cancer deaths is caused by the primary tumor. The vast majority of cancer mortality is caused by cells breaking away from the main tumor and metastasizing to other parts of the body, such as the brain, bones, or liver.
Though the United States has largely rejected the metric system, it is used for currency, as in 100 pennies = 1 dollar. Previously, the British currency system was used, with measurements such as 12 pence to the shilling, and 20 shillings to the pound.
Cancer has been around as long as humankind, but only in the second half of the twentieth century did the number of cancer cases explode.
![In the summer of 1793, a yellow fever epidemic struck Philadelphia, killing nearly 4,000. Tens of th](https://biology-forums.com/gallery/47/medium_374628_16_08_15_9_52_07_222511109.jpeg)
![The Kingsley plantation, on Fort George Island in Jacksonville, Florida. Zephaniah Kingsley, the own](https://biology-forums.com/gallery/47/medium_375552_19_08_15_9_09_52_223231620.jpeg)