Trachea Diffusion of oxygen and carbon dioxide takes place across the walls of the smallest tubes, called tracheoles, which penetrate tissues and even indent individual cells. Gas may be conducted through the respiratory system by means of active ventilation or passive diffusion. Unlike vertebrates, insects do not generally carry oxygen in their haemolymph. This is one of the factors that may limit their size. A tracheal tube may contain ridge-like circumferential rings of taenidia in various geometries such as loops or helices. Taenidia provide strength and flexibility to the trachea. In the head, thorax, or abdomen, tracheae may also be connected
Traditional Chinese medicines derived from the human body story, it would seem that those 'who go down to the silkworm room' [who are administratively sentenced to castration] should not be ignorant of this method, so I append it here." In some "Bencao gangmu" contexts concerning human drugs, Li Shizhen would accept the traditional theory but deny the contemporary practice. Under the human breath or "qi" section (52.23, tr. Luo 2003: 4176), Li says a "very effective" method for treating an elderly person who is suffering from cold and deficiency in the lower body is to have a boy or girl blow air through a cloth into the navel.