There's no liquid to speak of in sword fern. The nearby plant that is supposed to help with stinging nettles (as opposed to "dry nettles" that look similar but don't sting) is Equisetum, or horse tail (also called scouring rush). A very ancient plant.

If you want a good source of nitrogen in your diet, you can eat the nettles, but you have to boil them in water, drain it, and boil again. Much like the instructions you get for cooking skunk cabbage. Personally I can't say I'm tempted to try either. (For more of this information, look up the slim book on Ethnobotany by Erna Gunther).

SRS