LIFE OF ELIE METCHNIKOFF 81 



only a grave illness could save him, either by ending 

 in death or by awaking the vital instinct in him. 

 In order to attain his object, he took a very hot bath 

 and then exposed himself to cold. As he was coming 

 back by the Ehone bridge, he suddenly saw a cloud 

 of winged insects flying around the flame of a lantern. 

 They were Phryganidse, but in the distance he took 

 them for Ephemeridse, and the sight of them sug- 

 gested the following reflection : " How can the theory 

 of natural selection be applied to these insects ? They 

 do not feed and only live a few hours ; they are there- 

 fore not subject to the struggle for existence, they do 

 not have time to adapt themselves to surrounding 

 conditions." 



His thoughts turned towards Science ; he was 

 saved ; the Imk with life was re-established. 



