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Parkinson's disease is both chronic and progressive. This means that it persists over a long period of time and that its symptoms grow worse over time.
Pubic lice (crabs) are usually spread through sexual contact. You cannot catch them by using a public toilet.
The first-known contraceptive was crocodile dung, used in Egypt in 2000 BC. Condoms were also reportedly used, made of animal bladders or intestines.
Essential fatty acids have been shown to be effective against ulcers, asthma, dental cavities, and skin disorders such as acne.
Vaccines cause herd immunity. If the majority of people in a community have been vaccinated against a disease, an unvaccinated person is less likely to get the disease since others are less likely to become sick from it and spread the disease.
![The testes. In addition to producing sperm, the testes secrete the male sex hormones, primarily test](https://biology-forums.com/gallery/47/medium_14755_28_08_12_1_42_28_8238159.jpeg)
![The stages of labor and delivery. (A) During the dilation stage the cervix thins and dilates to 10 c](https://biology-forums.com/gallery/47/medium_14755_28_08_12_1_52_24_82561428.jpeg)