220 



effectually screened from ordinary air, and supplied solely 

 with calcined air, putrefaction never sets in. 



Putrefaction, therefore, he affirmed to be caused not by 

 the air, but by something in the air which could be 

 destroyed by a sufficiently high temperature. 



These results by Schwann were confirmed by the experi- 

 ments of Helmholtz in 1843, by Schroder and Von Dusch 

 in 1854, by Schroder alone again in 1857, and by Pasteur 

 in 1862. 



Experiments by Prof. Tyndall in 1868-9 went to show 

 that ultra-microscopic matter in the air was made visible 

 by a concentrated beam of light, and by the same test he 

 found that air that had been passed over the flame of a 

 spirit-lamp was optically pure, and when in this condition 

 that it had lost its power to generate life, and in this 

 manner gave complete confirmation to the announcement 

 by Schwann thirty years before. Tyndall's experiments 

 extended through several years, and demonstrated beyond 

 a doubt that infusions of meat, fish, and vegetables steri- 

 lized by heat, and freed from contact with common air, 

 never putrefies, while the same infusions exposed to com- 

 mon air were teeming with life in two or three days. 



In these experiments by Tyndall it was shown that the 

 rapidity of putrefactive development in infusions infected 

 by a speck containing Bacteria (developed germs) was 

 something extraordinary. The development in twelve 

 hours, with an infusion so infected, was equal to several 

 days' exposure where the infusion was only exposed to air 

 germs. This is most important, and should be noted, as it 

 will be referred to again, later on. It was also found that a 

 certain amount of oxygen was necessary to sustain Bacterial 

 life, while, on the other hand, experiments by Paul Burt, 

 proved conclusively that an excess of oxygen under pressure 

 would kill Bacteria. 



