This chapter will deal with the subject in as short and concise a manner as possible, with the object of giving the manufacturer a working knowledge of it that will help him in his everyday factory routine. Although volumes have been written about micro-organisms in food, it is not necessary for the packer of tomato products to have an accurate, detailed scientific knowledge of the subject in all its ramifications, but a general understanding of it will suffice for practically all purposes. What are molds, yeasts, spores, and bacteria? Are they animals or plants? Where do they grow, and under what conditions do they multiply most rapidly? Are they harmful, or are the kinds found in tomatoes all harmless varieties? If they are harmless, why does the government object to them? Why is a product containing a certain number considered all right, while when a larger number is present the product is said by the government to consist in whole or in part of a filthy, decomposed, putrid vegetable substance? Aren’t such foods as Roquefort cheese, cottage cheese, buttermilk, and sauerkraut fairly swarming with the same kinds of germs as tomato pulp? Aren’t these foods all considered healthful? Then why object to these germs in tomato pulp? Aren’t the germs all killed by the boiling, anyway? These are questions often asked by pulp packers, and it is hoped that the following will throw some light on the subject. Molds, yeasts, spores, and bacteria are very tiny plants, not animals. They are so small that they can only be seen by the naked eye when there are very large masses of them together, consisting, in the case of bacteria and yeasts, of hundreds of millions of small individual plants, and in the case of molds, of many individual mold plants closely massed together. You have all seen large tufts of white mold on tomatoes, and black mold covering a loaf of bread, but you probably did not realize the enormous numbers of individual mold plants that were present, or the rapidity with which they multiplied themselves. You have all seen swelled cans of tomato pulp, and after the cans were opened you have noticed the bubbles rising in the pulp, and have noted the very sour taste and often an extremely disagreeable odor. In every thimbleful of that sour pulp there were hundreds of millions of bacteria and yeast cells, so small in size that many thousand could collect at the same time on the point of a pin and they would not be noticed by the naked eye. It was these tiny bacteria and yeast plants which caused the physical and chemical changes in that pulp. Just as a parasitic vine winds itself around a tree and sucks the life out of it, so these millions of bacteria and yeast plants sucked all the goodness out of this tomato pulp, and left nothing but sour, decomposed tomato fiber, acid, and foul-smelling gas. Molds