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Most fungi that pathogenically affect humans live in soil. If a person is not healthy, has an open wound, or is immunocompromised, a fungal infection can be very aggressive.
The average human gut is home to perhaps 500 to 1,000 different species of bacteria.
The first successful kidney transplant was performed in 1954 and occurred in Boston. A kidney from an identical twin was transplanted into his dying brother's body and was not rejected because it did not appear foreign to his body.
Intradermal injections are somewhat difficult to correctly administer because the skin layers are so thin that it is easy to accidentally punch through to the deeper subcutaneous layer.
The first-known contraceptive was crocodile dung, used in Egypt in 2000 BC. Condoms were also reportedly used, made of animal bladders or intestines.