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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.
After a vasectomy, it takes about 12 ejaculations to clear out sperm that were already beyond the blocked area.
Immunoglobulin injections may give short-term protection against, or reduce severity of certain diseases. They help people who have an inherited problem making their own antibodies, or those who are having certain types of cancer treatments.
In 1835 it was discovered that a disease of silkworms known as muscardine could be transferred from one silkworm to another, and was caused by a fungus.
Vampire bats have a natural anticoagulant in their saliva that permits continuous bleeding after they painlessly open a wound with their incisors. This capillary blood does not cause any significant blood loss to their victims.