1. Higher fungi include mushrooms, toadstools, wood fungi, etc.

2. Molds consist of a dense mass of fibers. They produce spores or reproductive bodies which sometimes float in the air, settle upon organic substances and, if kept warm and moist and out of the sunshine, will grow and produce mold over the surface of the substance upon which they have settled.

3. Yeasts are visible only under the microscope. They are single-celled organisms, oval in shape. They reproduce by budding, producing a change in certain organic substances called alcoholic fermentation, by which alcohol and carbon dioxide are formed.

4. Bacteria are visible only under the microscope. They are much smaller than yeast plants. They are single-celled organisms, round, rod-shape, or spiral. They reproduce by fission, that is, by dividing in the middle, producing two individuals, or by spore formation. Bacteria are very abundant, being found everywhere. Some are disease-producing; many are non-disease-producing.

Most organic foods are injured or in time destroyed by the presence in them and growth of molds, yeast, and bacteria. To preserve food the growth of these organisms must be pre-vented. Fresh air and sunshine are nature's disinfectants and they check the growth of germs or even destroy them; hence the necessity of fresh air and sunshine in all parts of a house.

Molds, yeast, and bacteria are destroyed by heat and by certain chemicals. Their growth is checked by low temperature, by the removal of water, by the aromatic oils of spices, by an excess of sugar or salt, by the presence of smoke, and by certain acids. While such chemicals as formaldehyde, salicylic acid, benzoate of soda, will preserve foods indefinitely by destroying or checking the growth of germs, their presence even in very small amounts is harmful to the body, hence their use as food preservatives should be forbidden by the Pure Food Laws.