PART I. 



THE THEORY AND PRACTICE OF GENERAL 

 BACTERIOLOGY. 



CHAPTER I. 



INTRODUCTORY HISTORICAL REVIEW. 



THE sciences developed by mankind owe their early awakening 

 and subsequent growth to two entirely different sets of motives. One 

 of these is furnished by the necessities of life, in its everlasting struggle 

 for existence; the other by that intense desire of the human race to 

 unravel the mysteries of nature and solve the enigma of the origin 

 of life. 



That side of modern medical science which deals with micro- 

 organisms in relation to disease begins with attempts to recognize the 

 true nature and cause of disease and with experiments to ascertain 

 whether life can originate by spontaneous generation . The conception 

 that many 'diseases are due to microorganisms originating in or in- 

 vading the body, and multiplying therein, was first formulated long 

 ago, to be forgotten, and to be taken up again with renewed vigor 

 after the discovery that certain fermentative processes are due to these 

 minute bodies. This discovery wa's itself stimulated by the long- 

 continued experimental quarrel over the question whether or not 

 spontaneous generation of life occurred in fermenting and putrefying 

 organic materials. 



That diseases of mankind might be due to forms of life so small 

 as to be invisible was conceived as a purely hypothetical idea long 

 before the compound microscope had been invented. Varo, in the 

 first century before Christ, stated in writing that there might perhaps 

 exist animals so small that they could not be seen, but that might 

 enter the human body with the air through the mouth and hose and 

 so produce disease. Nothing, of course, but a mere hypothesis in 

 this direction could be formed before these microorganisms were seen. 



The first combination of lenses was constructed by Hans and 

 Zacharias Janssen, father and son, living in Holland in 1590. Their 

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