As has already been said, yeasts as well as molds belong to the colorless plants and fungi. The yeast which is used in making bread is a collection of thousands of tiny yeast plants, each of which is too small to be seen without the aid of a microscope. These plants are even less like ordinary plants than are the molds ; they consist merely of a single cell which appears, under the microscope, as a colorless oval. These yeast plants are so small and light that, like the spores of the molds, they float about in the air. Fruits preserved in sugar are especially apt to undergo a change which, as can be seen at once, is not due to mold growth. This is the action that takes place when preserves " work " or ferment, and it may occur also in jellies or syrups. Anything which contains sugar and water may show this change. The change is characterized by a sharp, pungent taste, and at some stages by the formation of bubbles through the liquid. Whenever these phenomena occur, it is a sign that growing yeasts are present. For yeasts, when they grow, are able to break up the sugar which is present and change it partly into alcohol, which gives the stinging taste, and partly into a gas called carbon dioxide, the escape of which through the liquid makes the bubbles. While yeasts are producing these results, they are mul- tiplying rapidly by a method called budding. In this 22 FOOD STUDY way new cells are formed which appear first as very tiny buds on the sides of the first cells and gradually grow larger and larger until finally they separate into independent cells. When active fermentation is going on, the yeast present is always found to be in this growing state. If, however, conditions are unfavorable, some yeast plants can form within each cell a number of spores, each of which is capable of developing again into a new plant. This spore formation usually happens if there is sufficient moisture present, but not enough food to produce growth. The air may be laden with these spores and even with some of the yeast cells themselves, as well as with the spores of molds. Other micro-organisms carried by the air are called bacteria. They are as simple in structure as the yeasts, and like them consist of single cells. They may, however, have three distinct shapes. Some are like little rods and are called bacilli (a bacillus, for a single one), others are like spheres and are called cocci, the third variety is spiral and is named spirilla (in the singular, spirillum). But all these, no matter what shape they may be, reproduce in the same way, and it is this method of reproduction which distinguishes them from the yeasts. Each cell grows a little longer than it was before and then breaks in two, each half being an individual. This process, known as reproduction by fission, gives to bacteria the name of fission fungi. Like yeasts, some bacteria can produce spores under unfavorable conditions. A bacterium, however, instead of producing a number of spores, forms only a single one. The advantage of the spore state seems to be in the greater power of resistance that the spore possesses — it is less easily killed by heat or cold or drying. If food is being sterilized and spore-forming bacteria are present, it is quite YEASTS AND BACTERIA 23

AI-modernized reading of the original text

As has already been said, yeasts as well as molds belong to the colorless plants and fungi. The yeast which is used in making bread is a collection of thousands of tiny yeast plants, each of which is too small to be seen without the aid of a microscope. These plants are even less like ordinary plants than are the molds ; they consist merely of a single cell which appears, under the microscope, as a colorless oval. These yeast plants are so small and light that, like the spores of the molds, they float about in the air. Fruits preserved in sugar are especially apt to undergo a change which, as can be seen at once, is not due to mold growth. This is the action that takes place when preserves " work " or ferment, and it may occur also in jellies or syrups. Anything which contains sugar and water may show this change. The change is characterized by a sharp, pungent taste, and at some stages by the formation of bubbles through the liquid. Whenever these phenomena occur, it is a sign that growing yeasts are present. For yeasts, when they grow, are able to break up the sugar which is present and change it partly into alcohol, which gives the stinging taste, and partly into a gas called carbon dioxide, the escape of which through the liquid makes the bubbles. While yeasts are producing these results, they are multiplying rapidly by a method called budding. In this way new cells are formed which appear first as very tiny buds on the sides of the first cells and gradually grow larger and larger until finally they separate into independent cells. When active fermentation is going on, the yeast present is always found to be in this growing state. If, however, conditions are unfavorable, some yeast plants can form within each cell a number of spores, each of which is capable of developing again into a new plant. This spore formation usually happens if there is sufficient moisture present, but not enough food to produce growth. The air may be laden with these spores and even with some of the yeast cells themselves, as well as with the spores of molds. Other micro-organisms carried by the air are called bacteria. They are as simple in structure as the yeasts, and like them consist of single cells. They may, however, have three distinct shapes. Some are like little rods and are called bacilli (a bacillus, for a single one), others are like spheres and are called cocci, the third variety is spiral and is named spirilla (in the singular, spirillum). But all these, no matter what shape they may be, reproduce in the same way, and it is this method of reproduction which distinguishes them from the yeasts. Each cell grows a little longer than it was before and then breaks in two, each half being an individual. This process, known as reproduction by fission, gives to bacteria the name of fission fungi. Like yeasts, some bacteria can produce spores under unfavorable conditions. A bacterium, however, instead of producing a number of spores, forms only a single one. The advantage of the spore state seems to be in the greater power of resistance that the spore possesses — it is less easily killed by heat or cold or drying. If food is being sterilized and spore-forming bacteria are present, it is quite YEASTS AND BACTERIA 23

Food study