6 INTRODUCTION 



of life in the flasks, the method of heating was applied to the 

 preservation of vinegar by Scheele (1782) and to the preser- 

 vation of foods in general by Appert (181 1). The method was 

 quickly introduced into other countries and developed by various 

 tradesmen, who attempted with more or less success to keep their 

 processes secret. Success in preservation by canning remained 

 somewhat uncertain, as a precise understanding of the underlying 

 scientific principles was still lacking. Schulze (1836) showed that 

 air might be admitted to flasks prepared by Spallanzani's method, 

 without the development of life and without putrefaction, pro- 

 vided the air were first passed through a series of bulbs containing 

 concentrated sulphuric acid. The subsequent work of Schroder 

 and van Dusrh (1853), who obtained similar success by filtering 

 the air through cotton, of Pasteur and Tyndall (1860-62) , who were 

 able to preserve putrescible fluids directly in contact with air, 

 provided the air were rendered perfectly free from dust, has 

 established the fact that the deconiposition ordinarily taking 

 place after exposure to the air is due to the introduction of living 

 germs into the previously sterile material. 



The idea that specific kinds of fermentation are caused by 

 specific kinds of microbes was first clearly put forward by Schwann 

 and Cagniard-Latour (1837), who showed that yeast-cells were 

 living organisms and claimed that the alcoholic fermentation of 

 sugar solutions was due to their growth. The importance of this 

 relationship received little recognition until Pasteur (1860-72), 

 during his extensive and careful researches into the nature of 

 fermentation and the causation of undesirable fermentation (dis- 

 eases of wines and beers), demonstrated conclusively that the 

 kind of decomposition of a fermentable substance depended upon 

 the nature of the substance, the kind of microbes present and the 

 environmental conditions, such as temperature and presence or 

 exclusion of air. The mere introduction of a small number of 

 unfavorable microbes was sufiicient to change the whole nature 

 and course of the fermentation. Furthermore, Van der Brock 

 (1857) and Pasteur (1863) were able to collect such fermentable 



