Although influenza is still far below its 1918-1919 level, we must not be complacent. Some signals are flying. The number of influenza cases. 82,951, reported by our State Department Health for the week ending December 18, 1943, was more than three times greater than the previous week and more than twenty-seven times that of the corresponding week in 1942. While the fight goes on, let us consider what advances have been made since 1918-1919 in the prevention and treatment of influenza and its ally, pneumonia.

A comparison of what was known then with our present knowledge reveals that we have made amazing progress. It was generally believed in 1918 that influenza and all of the pneumonias were of bacterial origin. The viral nature of epidemic influenza was first established in England in 1933, but t was not until 1938 that "virus pneumonia" was clearly recognized. Thus we are across the frontier of explorations that promise to push the range of medical knowledge at least as far as did the pioneer bacteriologic investigations of the last century.

What is meant by the viruses? To most people they are as mysterious as spells of primitive magic. In 1935, Wendell M. Stanley isolated the crystalline protein which is the tobacco virus. Here are substances which seem to stand on the dividing line between the animate and the inanimate, and as more is known about them our whole concept of "life" may well be changed. The fact that to "live"—that is, to multiply —viruses must be associated with living cells is of fundamental importance in our treatment of viral infections. Much of the mystery of the viruses may be attributed to their smallness. While learned theologians used to argue about how many angels could stand on the head of a pin, today it is the size of the viruses which absorbs those scientists who are competent to take such minute measurements by means of the electron microscope. To gaze upon the photograph of an influenza virus stirs the philosophic biologist to a deeper awe of nature and to a sharper impulse to investigate the laws which must control these atomies.

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Influenza exists in three forms: the world-sweeping pandemics such as that of 1918-1919, the epidemics such as we are now passing through, and the low-grade, constantly present or endemic form. It is from studies of epidemic influenza that the greatest progress has been made. It is plainly wrong to consider the flu as a war disease, although, as Edward Francis has noted, when virulent influenza coincides with the cruel shifts of population caused by war, the disease rises sharply.

What happens between epidemics is still a mystery. Richard E. Shope has discovered that the closely related virus of swine influenza can remain infective in the earthworm for as long as thirty-two months. Christopher H. Andrewes has suggested that human influenza viruses may have a basic, harmless form, in which they are harbored in human carriers and from which they become virulent. It is recognized that epidemics tend to recur every other year and that the present wave is not an example of spontaneous generation, but the continuation of what appears to be a cyclic pattern. This cycle has frequently run a course of thirty-three weeks. What effect the substitution of transcontinental and transoceanic aviation for caravan and ship will have on this cycle remains to be determined.