If a penny be dipped in vinegar and exposed to the air, and is then licked by a child, a certain amount of ill effect would undoubtedly ensue, but it does not follow that we should give up the use of copper money.

So, too, if we use tinned goods, and owing to our own carelessness or ignorance find occasionally that evil results ensue, we should not give up the use of the goods in question, but endeavour to find out the cause why these evil results follow only occasionally.
All good cooks know, or ought to know, that if they leave the soup all night in a saucepan the soup is spoilt.

Again, all housekeepers know that although they have a metal tank, they are bound to have a wooden lid on top, there being a law to this effect.

The point they forget in using tinned goods is this, so long as the air is excluded from the interior of the tin no chemical action goes on whatever.

When, therefore, they open the tin, if they turn out the contents at once no harm can ensue.
Unfortunately, there are many thousands who will open a tin, take out what they want, and _leave the remainder in the tin_.