THE BEGINNINGS OF LIFE. 337 



not have been much more reason for surprise ? We 

 ought therefore to be very cautious how we attempt to 

 set aside the conclusions which have been arrived at 

 on this subject founded as they have been upon direct 

 evidence of a most positive character. 



From this basis we may now proceed to enquire into 

 the nature and results of the experiments which have 

 been instituted with the view of throwing light upon the 

 origin of Bacteria and other similarly low organisms. 



The method of experimentation principally relied 

 upon since 1837 has been that introduced by Schwann 1 . 

 His experiments have been occasionally repeated with 

 some slight modification, whilst at other times he has 

 been exactly followed. In the latter case the solution 

 of organic matter is boiled in a flask, the neck of which 

 is securely connected with a tube closely packed with 

 portions of red-hot pumice-stone, or other incombustible 

 substance; and after the solution has been boiled for 

 some time, so that all the air of the flask has been 

 expelled, the flask itself is allowed to cool whilst the 

 tube containing the closely-packed red-hot materials is 

 still maintained at the same temperature, in order that 

 whatever air enters into the flask may be subjected to a 

 calcining heat as it passes through the tube. When the 

 flask has become cool, its neck is hermetically sealed by 

 the blow-pipe flame, so that it will then contain only the 

 previously boiled solution in contact with air (at ordi- 

 nary atmospheric pressure) which has been calcined. 



1 ' Annales de Poggendorf/ 1837, P- 184- * Isis,' 1837, p. 523. 



