Highlights in the History of Microbiology 27 



and sulfuric acid to filter out any suspended organisms. He 

 aspirated his flasks daily for three months, and at the end of that 

 period no flasks exhibited the slightest suggestion of microbial 

 growth. Theodore Schwann ( 1837 ) passed the air through heated 

 tubes before it was allowed to come in contact with his boiled 

 infusions, and he showed that growth was absent. Some biological 

 historians credit Schwann as founder of the science of disinfection. 

 It was only natural that opponents should accuse these two workers 

 of chemically devitalizing the air by the chemical treatment and by 

 the heating technics they employed. One of the greatest con- 

 tributions to microbiology resulted from this argument when 

 Schroeder and von Dusch (1853-1854) suggested the use of wool 

 stoppers in flasks to allow ready access of air without devitalizing 

 it in any way. These wool plugs are capable of mechanically 

 screening out the tiny microbes, and the bacteria-free atmosphere 

 can provide the necessary vital factors for growth of any organisms 

 present in the infusions. As long as these plugs are kept dry, they 

 are effective, but wet stoppers allow migration of organisms 

 through an otherwise effective filter. Today laboratories through- 

 out the world employ non-absorbent cotton as a standard pro- 

 cedure for stoppering test tubes and flasks to be used in the 

 cultivation of microorganisms. 



To add weight to Spallanzani's contention that microbes must 

 come from other microbes, he took a flask of broth containing: 

 actively growing bacteria, and he diluted this culture until only a 

 few bacteria were present in each drop of infusion. By placing 

 these drops under his microscope, he was able to observe that 

 simple method of reproduction which we now call binary fission— 

 equal splitting. These cells became longer, pinched in the center, 

 and finally separated into two organisms. He was probably the 

 first person to observe this process, but his keen observations were 

 for the most part lost in the many controversies relative to spon- 

 taneous generation. The pressure being exerted on science for 

 more and more proof of commonly accepted theories spurred 

 microbiological progress, just as the pressure of war results in 

 rapid expansion of practically all scientific knowledge. 



