Bacteria Induced Morphologic Changes.

Inoculation of Streptococcus sp. into germfree rats resulted in dramatic cecal changes within 24 hours. The weight of the cecum and its contents were reduced almost 50% and an apical aggregate of lymphatic tissue appears as a grossly visible entity, lacking only the more densely clumped nature of that found in classic rats. Exploratory work with mice confirmed this observation. Although the size (weight or surface area) of the cecal wall of the germfree rats is twice the size of that in classic rats, no change was noted when germfree rats were monoinoculated with Streptococcus sp. The cervical lymph nodes increased 3-fold following inoculation of germfree mice. This exploratory work illustrates the potential of gnotophoric animals in the study of defense mechanisms.