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Autoimmune diseases occur when the immune system destroys its own healthy tissues. When this occurs, white blood cells cannot distinguish between pathogens and normal cells.
During the twentieth century, a variant of the metric system was used in Russia and France in which the base unit of mass was the tonne. Instead of kilograms, this system used millitonnes (mt).
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.
Though methadone is often used to treat dependency on other opioids, the drug itself can be abused. Crushing or snorting methadone can achieve the opiate "rush" desired by addicts. Improper use such as these can lead to a dangerous dependency on methadone. This drug now accounts for nearly one-third of opioid-related deaths.
Adolescents often feel clumsy during puberty because during this time of development, their hands and feet grow faster than their arms and legs do. The body is therefore out of proportion. One out of five adolescents actually experiences growing pains during this period.
![Cranial capacity has increased approximately fourfold over the last 3.5 million years of hominin evo](https://biology-forums.com/gallery/47/medium_273688_23_02_15_7_07_16_2083771.jpeg)
![A passenger train crosses Stony Creek Bridge in the Rocky Mountains in 1878. Railroads were importan](https://biology-forums.com/gallery/47/medium_27_24_08_15_1_27_03_22389406.jpeg)