LIFE OF ELIE METCHNIKOFF 105 



he imagined that he ha^ solved all human ethical 

 questions. Much later, this fact led him to suppose 

 that death could actually be attended by agreeable 

 sensations. 



His robust nature, however, triumphed over all 

 these grave complications, and, during his convales- 

 cence, he was filled with a joy of living such as he 

 had never experienced before ; from that moment his 

 moral and physical balance was completely restored. 

 There was one impleasant sequel to his Ulness, an 

 acute affection of the sight (choroiditis), but it for- 

 tunately disappeared without leaving any traces, and, 

 in fact, he never suffered again from his eyes, in spite 

 of his constant use of the microscope. 



After his recovery he had a renascence of vital 

 intensity ; the life instinct developed in him in a high 

 degree ; his health became flourishing, his energy and 

 power for work greater than ever, and the pessim- 

 ism of his youth began to pale before the optimistic 

 dawn of his maturity. However, the relapsing fever 

 had very probably increased, if not started, the cardiac 

 trouble which eventually caused his death. 



During the time when IVfetchnikofi was forbidden 

 the use of the microscope on account of his eye weak- 

 ness, he studied Ephemeridse from the point of view of 

 natural selection. He wished to elucidate the manner 

 in which this selection operates during the very short 

 life of those insects : the rudimentary structure of 

 their buccal organs does not allow them to feed 

 themselves, and they have no time to adapt them- 

 selves to external conditions. 



During the 1875 holidays, at Gmunden and on the 

 Danube, he observed the nuptial flight of the may- 

 flies, a phenomenon which constitutes their short 



