A method of operating an avalanche photodiode includes providing an avalanche photodiode having a multiplication region capable of amplifying an electric current when subject to an electric field. The antibodies recognize viral epitopes which fail to elicit an immune response in man when encountered through infection or naturally through the environment. Then, a fixing member is made capable of fixing the mountain-shaped angle member in either a first attachment mode in which the angle member is in contact with the first wall portion and opposed to the connecting portion or a second attachment mode in which the angle member is in contact with the first wall portion and overhangs outward the first wall portion.