The historical assumption that the normal intestinal mucosa offers a 100 per cent effective barrier against absorption of bacteria is rapidly giving place to the conviction that gastro-intestinal microbic absorption is probably a normal physiologic function or, at least, a phenomenon that does not necessarily imply a local abnormality or lesion of the mucosa. The parenteral history of gastro-intestinally absorbed micro-organisms thus becomes a problem of normal physiology and is no longer of exclusive interest to pathologists. Arnold and his co-workers1 of the Illinois State Department of Health report convincing evidence that there is this normal physiologic bacterial absorption and suggestive evidence of a physiologic "cyclic circulation" of bacteria from the intestinal tract, through the systemic blood vessels, with fractional return to the intestinal lumen.
Arnold's experimental evidence was derived from fasting dogs. The abdomens of these animals were opened under ether anesthesia, and suspensions of B. prodigiosus were
REINFORCED ORAL VACCINES. JAMA. 1931;97(4):250. doi:10.1001/jama.1931.02730040032012
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