THE BEGINNINGS OF LIFE. 347 



Although the presence of air within the closed flasks 

 has generally been considered essential, still it had been 

 shown by Fray \ even before the time of Schwann, that 

 atmospheric air might be replaced by other gases, such 

 as hydrogen or nitrogen, and that even then (with the 

 method of closing the vessels at the time in vogue) 

 living organisms were subsequently to be met with in 

 the infusions. More recently Prof. Mantegazza 2 and 

 M, Pouchet 3 showed that oxygen gas might be success- 

 fully substituted for atmospheric air, in experiments 

 which in other respects complied with Schwann's con- 

 ditions j whilst Dr. Child 4 has also shown that organisms 

 are to be met with when either oxygen or nitrogen 

 is substituted for atmospheric air in similar experi- 

 ments. He failed to get any positive results, how- 

 ever, in the presence of carbonic acid or hydrogen 

 gases. 



On the other hand, it was thought by Burdach 5 that 

 organisms were not procurable unless the hermetically- 

 sealed flasks contained a certain amount of air. He 

 says : c Gruithuisen discovered that infusions, other- 

 wise very prolific (those of hay, for example), did not 

 yield infusoria in glass vessels in which the stopper 

 touched the surface of the fluid/ In a comparatively 



1 'Essai sur 1'origine des corps organises et inorganis^s,' Paris, i8ai, 

 pp. 5-8. 



2 ' Giornale. dell. R. Istituto Lombardo,' t. iii., 1851. 



3 ' Compt. Rend.' (1858}, t. xlvii. 



4 ' Essays on Physiol. Subjects,' 2nd ed., 1869, p. 114. 



8 Traite de Physiologic ' (Transl. by Jourdan), 1837, t. i p. 16. 



