Testicles are located in the scrotum, one on the left and one on the right. Generally the left side is slightly lower than the right side 1cm. Testicles are slightly oblate and oval with smooth surface, which are divided into medial and lateral sides, anterior and posterior edges and upper and lower ends. Its frontier is free; There are blood vessels, nerves and lymphatic vessels in and out of the posterior margin, which are in contact with epididymis and testis of vas deferens. The upper end and trailing edge are attached to the epididymal head, and the lower end is free. The outside is convex and the inside is flat. Testicles grow rapidly with sexual maturity, and shrink and become smaller with the decline of sexual function in old age.
Testitis is usually caused by bacteria and viruses. Bacterial infection rarely occurs in testis itself, which is due to the abundant supply of blood and lymph in testis and its strong resistance to bacterial infection. Bacterial orchitis is mostly caused by inflammation of the adjacent epididymis, so it is also called epididymal orchitis. The common pathogens are Staphylococcus, Streptococcus, Escherichia coli and so on. Viruses can directly invade testis, the most common one is mumps virus, which itself mainly invades children's parotid gland.