The present book is a bacteriologic investigation that was made at Camp Pike, Arkansas, during the period of the influenza epidemic from September 6 to December 5, 1918.The outbreak of scattered epidemics of influenza beginning in 1915–16 and finally culminated in the pandemic of 1918–19.Influenza in epidemic form also made its appearance in the army camps of the United States during March, 1918. Pneumonia followed the epidemics of influenza which occurred in the spring of 1918 and exhibited characters similar to those of the pneumonias which followed the pandemic of September and October, 1918. Influenza became epidemic in Spain about the middle of May and in other countries received the name "Spanish influenza" which is not more applicable than the designation "Russian influenza" often applied to the disease during the pandemic of 1889–90.