The substances which bring about these changes are called ferments, and their results are called fermentations. If these fermentations occur in foodstuffs, their character and quality are so changed for the worse (with few exceptions) that they are quite unfit for human food. It may be argued that wine and beer are both the products of fermentation, but that when taken in moderation they are wholesome drinks. In both these cases the process of fermentation is watched; it proceeds under carefully supervised conditions, and is checked at a definite point and moment. Besides which there are countless varieties of these micro-organisms some of which cause fermentations useful to man, while others are dangerous to his health.