The new interest in calfhood vaccination against Bang's disease is bringing out some interpretations, both of field observations and experimental data, that require the closest scrutiny if we are to evaluate correctly the effectiveness of artificial immunization. Certain fallacies and half-truths have for years beset the publications dealing with all preventive measures used against the disease, and it may be helpful to point out a few of these as we approach the flood of reports on calfhood vaccination that is sure to appear in the near future.