The chapter opens with a description of the reaction of a white blood cell to a foreign invader's presence in a nearby lake. The white blood cells are shocked to learn that the invader has entered through a nearby drain port, which transports carbon dioxide and oxygen to the body. They also learn that there is a "swish antigen" detected in their own blood, which they believe to be an ancient "weapon" that they have been using to protect themselves against foreign invaders. They are horrified to discover that the invaders are coming from the same lake that they used to protect their own body from. The narrator explains that the "secret weapon" is an antibody produced by a type of lymphocytes called a "b cell" that makes weapons to fight antigens, such as those of bacteria and viruses. The b cell explains that mast cells release a chemical called histamine when they recognize a foreign substance or damage to a tissue. They believe that the release of this chemical is the cause of the "volcano reactions" , which are caused by the sneeze of histamines, which stimulate the nerves of the nasal mucosa.