The fundamental basis for the microscopic examination of any food product must depend upon the structure of the material which enters into its composition. Any attempt to determine an abnormal condition, such as decomposition, without a knowledge of the normal, must necessarily be of little value. There is some work which can be done in a mechanical manner by almost anyone capable of looking through a microscope, and if the work is properly supervised, it may have a value, but the lines along which this can be done are very limited. Any attempt to apply such superficial methods to the general examination of food products can not properly protect the public and may be unfair to the producer. It has, therefore, been deemed advisable to incorporate a brief statement concerning the structure of the tomato before discussing the resultant products. HISTOLOGY OF THE TOMATO AND OF THE RESULTING KETCHUP. STRUCTURE OF THE TOMATO. =Pericarp.= The tomato is a typical berry, the ovary wall, free from the calyx, forming the fleshy pericarp, which encloses chambers filled with a clear matrix, containing the seeds. The pericarp consists of an outer tough membrane, the epidermis, a more or less thick layer of parenchyma tissue, the pulp, and an inner thin, delicate membrane, the lining layer of the loculi or chambers in which are the seeds. The epidermis consists of a single layer of cells which have a very thick continuous cuticle about one-half of the diameter of the whole cell. The cuticle differs in chemical composition from the rest of the cell walls, being impervious to water, and resisting rotting longer than do the cellulose walls. As it is continuous over the whole of the fruit, the skin can be readily separated from the other tissues. Hot water facilitates the removal of the skin, as it causes the cellulose of the walls to swell more than the cuticle, producing an effect as of shrinkage of the outer wall and a consequent curling of the skin. The radial walls of the epidermis are short and irregularly thickened, leaving pits in the walls, and giving them a beaded appearance. The skin constitutes about 1.3 per cent of the tomato. The layers of parenchyma just beneath the epidermis are closely united and flattened, with their adjoining walls irregularly thickened. On account of their position, they are called hypoderm. In the tomato the hypoderm consists of two or three layers of cells, parts of which usually separate with the epidermis. Below these cells are the thin-walled parenchyma cells, which are approximately globular, vary considerably in size, are very loosely held together, and have many intercellular spaces. These cells constitute the mass of the pulp, and with the juice constitute 96.2 per cent of the tomato.