render the atmosphere of that room unpleasant and unwholesome ; or just as much as a 

 garment worn next the skin becomes dirty from the perspiration with which it is in 

 contact, so these minute living things bring about changes in their surroundings by their 

 active life. 



The substances which bring about these changes are called ferment*, and their 

 results are called fermentation*. 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. 



One property possessed by these ferments is the source of considerable trouble to 

 the housewife, and that is their capacity for producing effects out of all proportion to 

 the amount of ferment present. It is not the quantity of ferment produced in a joint 

 of meat by these mischievous germs which taints the whole ; the widespread chemical 

 changes, which render it unfit for food, may be brought about by a microscopic particle 

 of the offending substance. 



MOULDS AND YEASTS AS AGENTS OF DECAY. 



Moulds also bear their part in causing food to be unpalatable, if not unwholesome , 

 and yeast-plants grow freely in thin syrups, for instance ; hence the fermentation which 

 sometimes takes place in carelessly bottled fruit. 



Thus decay in any of its varied forms may actually render food poisonous ; it 

 certainly makes it less wholesome ; it spoils its appearance ; and assuredly it leads to 

 much waste of what should be good nutritious material. 



(Fio. 3.) 



A dirty practice, which conduces to 

 the decay of food in households where 

 it is permitted. 



SUMMARY. 



(1.) Decay is the work of living organisms or of the results of their active presence 

 in food substances. 



(2.) Necessary to their activity is suitable food, suitable temperature, and sufficient 

 moisture. 



