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Abstract

An electron microscopic study has been made of the constituents of the lamina propria of the stomach, small intestine and large intestine of the mouse. This layer is highly cellular in the intestines, less so in the stomach. The connective tissue cells are often crowded together without detectable fibers or ground substance between.

Below the basement (boundary) membrane of the epithelium attenuated fibrocytes form an almost continuous layer. The appearance of a fibroblast in mitotic division is described.

In the connective tissue spaces are abundant plasma cells, macrophages, undifferentiated cells and eosinophils. The fine structure of each is described and illustrated.

Particularly evident is the frequency with which plasma cells lie in direct contact with macrophages and with eosinophils. In some instances, vesicles of similar appearance occur in apposed plasma cell and macrophage, suggestive of exchange of material.

These close relations of macrophages, plasma cells, and eosinophils are discussed in terms of the role each plays in the defense of the organism against foreign antigens.