12 THE CANNING OF FOODS. 



STERILIZATION. 

 HISTORICAL NOTE. 



The present status of our knowledge of canning is based on the 

 modern science of bacteriology. The invention of the compound 

 microscope and its many improvements has revealed the presence 

 of minute vegetable organisms in the air, in water, and on everything 

 with which we come in contact. These organisms are bacteria, yeasts, 

 and molds, and are present either in their vegetative or spore state, 

 being the " eggs " which Spallanzani thought were in the air. 



Bacteria and germs were first seen in 1683 by Leeuwenhoek, who 

 constructed a crude compound microscope. He knew nothing of 

 their character nor of their relation to higher organisms, but as 

 many of them were motile he regarded them as animals, and from 

 their habitat named them " infusoria." Almost nothing further was 

 discovered until 1786^ when O. F. Miiller described some of the 

 structural characters. Another lapse occurred until 1838, when Ehren- 

 berg published a work upon the so-called infusoria, in which he 

 added to and systematized the information to date, some of his names 

 being still used. Dujardin, Perty, Cohn, and Nageli added much to 

 the knowledge of the structure and life habits of micro-organisms, 

 but none of these associated the organisms with any economic 

 problem. 



Pasteur, about 1860, was the first to discover that these organisms 

 were the cause of the changes known as fermentation ; also the cause 

 of the supposed spontaneous generation. He recognized that they 

 had a definite relationship to economic activities and later he ap- 

 plied the knowledge gained in the laboratory in a practical way to 

 many industries. He discovered that by heating certain food prod- 

 ucts to a certain degree and for a certain period the time of keeping 

 might be prolonged. The principle had a practical application to 

 many substances on which boiling would have an objectionable effect 

 and is taken advantage of on a large scale in wine and beer making 

 and in dairying. He found further that by heating and cooling at 

 intervals, as on successive days, sterilization might be accomplished ; 

 also that the organisms on different substances had varying resistant 

 powers to heat and that in intermittent heating different tempera- 

 tures must be employed, according to the predominating organism. 

 All of the fundamental principles that Pasteur discovered have an 

 important relation to canning. 



In 1876 Dr. Robert Koch discovered the relation of specific germs 

 to diseases, and a few years later elaborated methods for separating 

 germs into pure cultures. Since that time progress has been rapid 

 and the relation of various organisms to the different industries has 

 become fully established. 



