Food study

tion of water, and it is only in watery foods that they are capable of much growth. Sugar and flour, for example, are much too dry for them. Twenty-five to thirty per cent of water is necessary for any growth, and, even then, it will not be vigorous. Most bacteria cannot grow in foods which are strongly acid, but molds do not mind the acid, and as only small percentages of moisture are necessary to keep them alive, in damp weather as dry a food as flour may become moldy. Even books and clothes may mold in a damp room. Mildew is one species of mold. Bread that is in a closed bread-box is apt to become moldy if left too long ; but if bread is spread out, exposed to the air, it will probably dry without any molding at all. Possibly this is because a moving current of air dries up the moisture ; but, whatever the reason, it is true that mold grows best in still air. Bacteria differ greatly in relation to air. Some grow only in the presence, others in the absence of it, and some can prosper either way. The bacteria that live without air cause putrefaction and are perhaps most likely to produce ptomains; but the majority of bacteria grow best in an abundance of air, and most foods begin to spoil on the surface. Direct sunlight rapidly kills bacteria, and any daylight makes them grow more slowly and less vigorously. Molds may grow in either light or darkness, but they, too, grow best in a dark place. Plenty of light and fresh air, then, are the housekeeper's allies in the fight against microorganisms. Another method of checking the growth of microorganisms is by means of low temperatures. Few organisms can make any but the most feeble growth in the cold. Even rather slight differences in temperature seem to have surprisingly great effects. For this reason food is placed in an ice-box to delay the growth of the micro-organisms, but as the temperature, even in very well-constructed refrigerators with a large ice chamber, is forty to forty-five degrees, usually nearer fifty degrees Fahrenheit, growth can be delayed only for a limited time. Such food will spoil eventually. But a temperature even of sixty degrees is still a great aid in keeping food temporarily. Cold storage is more efficient than home refrigeration, because a lower temperature is used. There are other means of preserving food, besides the use of cold temperatures. Drying evidently prevents the growth of bacteria, since they need so much water, and, if this is thorough, it may also prevent mold action. Dried fruits of all kinds have long been used, as have also some dried vegetables. Lately, more kinds of dried vegetables have been put upon the market, and even desiccated soups. All these are good food, as nutritious as before drying, but they do not retain quite the original flavors. Foods which can be boiled and canned may be made truly sterile, and if the process is carried out properly, such materials will keep indefinitely. Fruits and vegetables may well be taken care of in this manner.