Numerous contradictions in the epidemiologic teachings regarding influenza would have been avoided if the writers had recognized that the pandemics which affect the whole world do not follow the same epidemiologic laws as their sequels, or local endemic epidemic outbreaks.

The most important characters of pandemic influenza are:

1. The appearance of true pandemics at considerable intervals of time-occasionally several decads apart.

2. The usually demonstrable origin of the pestilence from some particular portion of the world.

3. Rapid spread over countries and hemispheres.

4. Extensive affection of the inhabitants in the locality of outbreak.

5. Rapid disappearance of the disease after an existence of several weeks.

6. Entire independence from wind and weather, from season, climate-in short, from all atmospheric telluric conditions.

7. Disproportion between enormous morbidity and remarkably small mortality.

8. The uniformity with which all ages and occupations are affected.

A detailed investigation of these characteristics of pandemic influenza relieves us from devoting a special section to the ancient controversy: "Contagium or miasma?" This question finds its own solution in the following description, in which the doctrine of the contagious nature of influenza will be fully confirmed.