After Carmel’s comment above I decided to find out what Mark was referring to by actually reading that page. Interesting reading although a bit too much for 9am in the morning here so I found this page and this one that explain the following:

The laws of chemistry state that there is a limit to the dilution that can be made without losing the original substance altogether. This limit, which is related to Avogadro’s number (6.023 x 1023), corresponds to homeopathic potencies of 12C or 24X (1 part in 1024). Modern proponents claim that even when the last molecule is gone, a “memory” of the original substance is retained. A 30X dilution means that the original substance has been diluted 1,000,000,000,000,000,000,000,000,000,000 times. Assuming that a cubic centimeter contains 15 drops, this number is greater than the number of drops of water that would fill a container more than 50 times the size of the earth and a 30C solution would require a container more than 30 billion times the size of the Earth.

For practical purposes, this means that “30X” and “30C” solutions do not actually exist, because it is not possible to create a solution in which one molecule of an original substance is dissolved in a container of water bigger than the Earth.

So much for that 30C Arnica they recommended in the maternity hospital.