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Human neurons are so small that they require a microscope in order to be seen. However, some neurons can be up to 3 feet long, such as those that extend from the spinal cord to the toes.
Adult head lice are gray, about ? inch long, and often have a tiny dot on their backs. A female can lay between 50 and 150 eggs within the several weeks that she is alive. They feed on human blood.
Cyanide works by making the human body unable to use oxygen.
Long-term mental and physical effects from substance abuse include: paranoia, psychosis, immune deficiencies, and organ damage.
According to the National Institute of Environmental Health Sciences, lung disease is the third leading killer in the United States, responsible for one in seven deaths. It is the leading cause of death among infants under the age of one year.
![To examine a child’s ear, the pinna should be pulled back and up for children over 3 years; the pinn](https://biology-forums.com/gallery/47/medium_14755_07_10_12_3_29_39_93452079.jpeg)
![H. erectus migrated out of Africa beginning about 1.8 million years ago and is first known from Geor](https://biology-forums.com/gallery/47/medium_275510_22_02_15_5_56_58_207731480.jpeg)