MICRO-ORGANISMS or Microbes. Within the scope of this subject come a large number of minute forms of vegetable life of the fungi order. Those which affect human foods and digestion may be divided into three classes under the titles of Molds, Yeast and Bacteria. The appearance of Molds, or moldiness, is familiar to everyone. Yeasts are too small for single specimens to be seen without the aid of a microscope, but in a mass, of hundreds of thousands or millions, they are handled by the general public in the form of yeast cakes. Bacteria are still more minute and the average consumer never attains a personal acquaintance with them, but the effects of their existence are observable all around him. Molds propagate by means of spores or seed dust ; Yeasts produce new cells by "budding," and Bacteria principally by the division of mature cells. With a few exceptions, Molds seem to serve no good purpose in the human food supply. Yeasts are responsible for all kinds of fermentation (as popularly under stood), both desirable and otherwise. To Bacteria is due much of the enjoyable flavor of many of our foods, but their uncontrolled presence is the cause of all real putrefac tion and decay.
Mold spores and Yeast and Bacteria cells are present everywhere—the middle of the ocean, the center of a desert and regions of extreme cold alone excepted—and are especially numerous in the vicinity of human habitations. Any food into which they fall,
if it affords suitable soil and temperature, is speedily rendered unfit for human use—in spite of their value under certain conditions—hence the danger of exposing foods to the atmosphere, the advisability of the speedy consumption of fresh foods and the importance of the cold-storage and canning industries. It is not any poisonous qual ity in the microbes themselves that accomplishes the damage—for with a few excep tions they are entirely harmless to the human system—but their growth, multiplica tion and life in food, change and break down its chemical structure and render it unsuitable and finally unfit for use. Cold storage retards the growth of all micro organisms, and canning may be briefly described as the science of destroying by sterilization all those contained in the food used, and preventing by hermetical seal ing the entrance of any others.
Special articles on each of these three classes of microbes will be found under their respective titles—Bacteria, Molds, Yeasts.
The word "mold" is not an accepted botanical expression, but it is employed as a useful term, widely used and understood, for describing the thread-like, branching fungi, the largest of the micro-organisms referred to in this article, which produce "moldiness." "Yeast" and "Bacteria," as here employed, are true botanical terms.