INTRODUCTION 23 



From the time of the experiments of Spallanzani until 

 as late as 1836 but little advance was made in the elucida- 

 tion of this, at that time, obscure problem. 



In 1836 Schulze attracted attention to the subject by 

 the convincing nature of his investigations. He showed that 

 if the air which gained access to boiled infusions be robbed 

 of its living organisms by first passing it through strong 

 acid or alkaline solutions no decomposition occurred, and 

 living organisms could not be detected in the infusions. 

 Following quickly upon this contribution came Schwann, 

 in 1837, and somewhat later (1854) Schroder and Dusch, 

 with similar results obtained by somewhat different means. 

 Schwann deprived the air which passed to his infusions of 

 its living particles by conducting it through highly heated 

 tubes; whereas Schroder and Dusch, by means of cotton- 

 wool interposed between the boiled infusions and the outside 

 air, robbed the air passing to the infusions of its organisms 

 by the simple process of filtration. In 1860 Hoffmann and 

 in 1861 Chevreul and Pasteur demonstrated that the pre- 

 cautions taken by preceding investigators for rendering 

 the air which entered these flasks free from bacteria were 

 not necessary; that all that was required to prevent the 

 access of bacteria to the infusions in the flasks was to draw 

 out the neck of the flask into a fine tube, bend it down along 

 the side of the flask, and then bend it up again a few cen- 

 timeters from its extremity, and leave the mouth open. The 

 infusion was then to be boiled in the flask thus prepared 

 and the mouth of the tube left open. The organisms which 

 now fell into the open end of the tube were arrested by the 

 drop of water of condensation which collected at its lowest 

 angle, and none could enter the flask. 



While, from our modern standpoint, the results of these 



