The truth about dirt

As adults we spend hours trying to get rid of dirt. We sweep, mop, dust, do the laundry and wash our hands. We wage a constant battle against the stuff, sometimes we win, sometimes we loose. Now that I have a toddler I seem to loose a lot more than I win. He absolutely adores the stuff. I don't know if it's a boy thing or just a baby thing, but he can't get enough. He loves to dig in it, feel the sand run between his fingers, rub it through his hair. He enjoys filling up his bucket with it (or my shoe), he enjoys digging holes and splashing in the mud. At the end of most days his cloths are so dirty I can't distinguish what colour they  originally were. His favourite thing about dirt though, is eating it. I don't know what it is about the stuff that makes it look so damn tasty but he can't get enough. We'll be working in the garden and before I know it he will have shoved a handful in his mouth. The worst part is, he seems to enjoy the taste, even going back for seconds if he has the chance. I just hope that eating dirt has no long term side effects, its suppose to build up the immune system right? If thats the case then Finn should be free from colds this winter. I understand that babies explore the world through taste, but can't he be satisfied with just one bite?