These circulate through the bloodstream and enter and reside in lymph nodes. They then circulate through the bloodstream, and are deposited in the brain. Endocrine glands secrete substances that circulate through the blood stream. In nature, influenza viruses circulate continuously among animals, especially birds. They are good convective inhibitors because air cannot circulate through the lattice. Particles traveling faster or slower will not circulate in the desired fashion. Qi is said to circulate in the meridians. Hormones circulate in higher concentrations, and tend to be made by specific kinds of cells. There are few buses and these do not circulate according to a fixed timetable. As gas atoms circulate around the system they enter the cavity. Such particles could circulate in the oil and grind against moving parts, causing wear. The sea currents circulate in the counterclockwise direction. Unlike money, vouchers cannot circulate and are not transferable between people. The entry featured a monumental ramp and columns that allowed the air to circulate. These notes will circulate alongside the existing notes.