Colloidal silver is a natural antibiotic that can be taken internally or used externally on wounds, burns, etc. It even kills antibiotic resistant "super germs" (MRSA.) Colloidal silver is a great natural medicine for survivalists and is easy to make at home using inexpensive equipment. This video explains how you can make your own colloidal silver for pennies a gallon.
I show this video to show how to make your own in a SHTF situation. I USUALLY buy my silver from Nature's Sunshine because their product "Silver Shield" is made from the patented Silver Sol process and is superior.
Be Careful When Making Colloidal Silver - Red Flags
4th UPDATE 12/19/15
After 5 years I've only had one mild cold and CS has successfully prevented flu symptoms and other illnesses from taking hold. I ride a bike in 40 degree weather sometimes! I now use the machine sold at SilverEdge dot com by Steve Barswick that has superior quality CS.