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After a vasectomy, it takes about 12 ejaculations to clear out sperm that were already beyond the blocked area.
There are 60,000 miles of blood vessels in every adult human.
The average human gut is home to perhaps 500 to 1,000 different species of bacteria.
IgA antibodies protect body surfaces exposed to outside foreign substances. IgG antibodies are found in all body fluids. IgM antibodies are the first type of antibody made in response to an infection. IgE antibody levels are often high in people with allergies. IgD antibodies are found in tissues lining the abdomen and chest.
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.