308 THE NEW WORLD OF SCIENCE 



same disease, although the laboratory proof is still lacking, be- 

 cause the clinical course of an attack of the disease is so charac- 

 teristic. 



What is the history of influenza in inter-epidemic years? 

 In the absence of complete proof it is impossible to be sure 

 about it, yet the most commonly accepted belief is that the 

 disease is always with us, as the ordinary influenza, a form of 

 common cold, but that only under exceptional circumstances 

 does it become virulent and cause any appreciable mortality. 

 Dr. Welch showed years ago that the influenza bacillus could 

 be recovered frequently at autopsy from the cavities in tuber- 

 culous lungs. Others have shown its presence in chronic dis- 

 eases of the sinuses accessory to the nose and throat. In other 

 words, the causative organism is regularly present, but of low 

 virulence, and it does not prove sufficiently fatal to cause an 

 appreciable influence on the annual mortality curves. Why 

 some diseases, such as infantile paralysis and influenza, should 

 suddenly become extremely virulent and produce wide-spread 

 epidemics we do not now know. During the war it is probable 

 that it obeyed the same law as measles, and spread among our 

 soldiers because they were young, many of them from the 

 country districts, and, therefore, not immune to the infection. 

 As the conditions were ideal for the rapid passage of the virus 

 from man to man, it is concluded that there was a steady 

 increase in virulence, until the virus was capable of causing 

 a very severe and fatal illness. 



During the last four months of 1917, when the camps were 

 filled with recruits, there were reported 40,512 cases of influ- 

 enza, yet it was not noted as a severe disease, and it was not 

 apparently followed by pneumonia to any serious extent. In 

 the Winter and Spring of 1918, particularly in January, March 

 and April, many cases of influenza were again reported, as well 

 as many fatal cases of pneumonia. It was not until the Fall, 

 however, during September and October, that it was recognized 

 that the fatal epidemic form of influenza was present, and that 

 pneumonia was reported as a frequent and fatal complication. 



