[Illustration: Respiratory Disease at Army Camps] This experience was equally true during the Civil war. Although there are no exact reports, it appears that measles prevailed in the Confederate army and was much more highly fatal than in the Union army. A recurrent influenza epidemic usually takes the form of a secondary wave, particularly so if it follows the primary wave within a short period of time. The difference in the character of the wave is due to the fact that there is still a comparatively large concentration of immune individuals, immunized by having had the disease during the primary spread. The secondary type of the influenza wave corresponds with the measles curves for the urban camps. There are all gradations in influenza from the typical primary wave down to a very much flattened wave of relatively long duration, and even on to the stage of endemicity, with no discernible wave. In 1920 the recurrent epidemic partook more of the form of a primary wave, because in most individuals the period of immunity had been completed by January and February, 1920. If we could, by some means, induce an immunity which would last for long periods of time, pandemic influenza would disappear from the earth and the disease would be relegated to the comparatively minor position now occupied by measles. The disease would be constantly endemic, frequently breaking out in small epidemics, but never becoming pandemic. This is one object that should be held in view by the immunologists and bacteriologists. But it is not so simple. Even were a successful vaccine discovered, it is doubtful whether any considerable group of the population could be persuaded to take it as often as would be necessary. Universal vaccination against small pox has never been carried out. The same would be true at the present time with regard to influenza. There is another similarity between measles and influenza. Measles is as infectious as is influenza. It is as readily transmitted and the mode of transmission is probably the same or very similar. In both diseases we are made poignantly aware of the great contagiousness of the disease, and yet in neither disease has there ever been conclusive evidence of experimental transmission from man to man. Several have reported attempts to transfer measles, but in each case the evidence of infection has been incomplete. The work of Hektoen has been quoted in particular, but Sellards, after carefully reviewing his work, concludes that the evidence of infection is insufficient. Moreover Hektoen’s patients were not exposed subsequently to measles infection in the natural way. SECTION VIII. THE PREVENTION AND CONTROL OF INFLUENZA.