120 EXPERIMENTAL EVOLUTION LECT. 



same process which is injurious to life, as in Gratacap's 

 experiments, 1 considerable differences are easily 

 perceived, though not explained. While the common 

 fly withstands living in pure oxygen less than thirty 

 hours, Doryphora decemlmeata survives easily for 

 three whole days, and Colias phyllodoce cannot stand it 

 more than twelve hours. While the same DorypJiora 

 can live twenty-four or even forty-eight hours in pure 

 hydrogen, a species of Noctua cannot live more than 

 twenty minutes, nor Poinpilns unifasciatus more than 

 ten minutes. Why, we cannot tell, but there cer- 

 tainly is some physiological and chemical reason 

 accounting for the fact. 



Every physiologist knows well that the same poison 

 exerts very different influences on different organisms. 

 For instance, while brucine acts on dog or frog in the 

 same manner as strychnine (although stronger doses 

 are required than of the latter) it acts very differently 

 on the common crab (Carcinus maenas}, which exhibits 

 no convulsions but only a peculiar movement of the 

 external mouth-parts. Picrotoxin, similarly, acts on 

 dog and frog like strychnine ; on the crab it induces 

 a powerful contraction which is most characteristic. 2 



1 Gratacap, Vitality of Insects in Gases* American Naturalist, vol. 

 xvi., 1882, p. 1019. 



2 Cf. Henry de Varigny, De t Action de la Strychnine, de la Brucine 

 et de la Picrotoxine sur le Carcinus maenas. Journal de V Anatomic et 

 de la Physiologic, 1889, Paris. Also : H. de Varigny and Paul Langlois, 



