Nettle stings than?

In these photos you can see stinging nettle machine. Hair nettle - hollow inside and quite fragile (there high content of silica), especially the tip. Young hairs on the end there is a little more spherical the bulb. Lower thickened part - quite flexible pouch with burning formic acid. When slightly hurt a hair, its tip carrying the bulb breaks off easily, with a very sharp bend it turns, it fits easily into the skin. Very similar to the way the breaks off the tip of a glass ampoule. By a hair-tube and extruded liquid from the bottom of the pouch is wrinkled. In general, in a single device and a vial and a syringe. Here are stinging nettle cells.