102 SCIENCE REMAKING THE WORLD 



valescence. Characteristic of an epidemic is the rapid 

 spread, coupled with a high incidence of infection, so 

 that more than half a population may be attacked in 

 the first wave, and the recurrence of successive waves 

 of diminishing extent and severity until, in the course 

 of three or four years, the epidemic dies out. 



EXPERIMENTAL INOCULATIONS. In September, 1918, 

 when it was decided to undertake a search for the in- 

 fectious agent of epidemic influenza in the laboratories 

 of the Rockefeller Institute for Medical Research, 

 methods of transmitting the infection to animals were 

 first considered, because an experimental infection in 

 animals offers facilities for study not obtainable in 

 human cases. For example, the transmission of a 

 transient disease such as influenza through animals 

 insures its indefinite propagation and affords material 

 for study after human sources fail. An infection in 

 laboratory animals can be interrupted at any time for 

 necessary examinations of its progress and offers many 

 avenues of approach which are closed to the investigator 

 if he must depend wholly upon human cases for study. 



Uncomplicated influenza, however, is a relatively 

 mild disease in man and some of its prominent manifes- 

 tations such as chills, headache, sore throat, and de- 

 pression cannot be observed in animals. It was ex-i 

 pected that the experimental disease, if successfully 

 established in animals, would be mild as well, and 

 might be missed unless some definite, measurable cri- 

 teria could be employed to indicate the development of 

 abnormal conditions similar to those observed in human 

 <:ases. It was thought that among the characteristic 



