28 THE FUNDAMENTAL PRINCIPLES. 



What is the eye-point ? 



What care should be given to a microscope ? 



Describe the tests for determining the cause of an obscure image 



Describe the methods of cleansing the lenses of the microscope. 



Describe a condenser for dark field illumination. 



CHAPTER I. 

 THE FUNDAMENTAL PEINCIPLES. 

 THE HISTORY OF BACTERIOLOGY. 



WHEN in the latter part of the seventeenth century 

 Anthony von Leuwenhoek, by means of his magnifying- 

 glasses, first discovered organisms in decaying vegetable 

 infusions, he may be said to have laid the very first stone in 

 the foundation of what later on was to be the Science of 

 Bacteriology. 



It was very long after this, however, before sufficient facts 

 were collected to place this science upon a firm basis, and it 

 remained for a genius like the immortal Pasteur and the 

 eminent talents of the equally great Koch to build up the 

 superstructure of bacteriology so as to have it accepted by 

 all as the true basis of scientific medicine. 



When first observed, these microorganisms were supposed 

 to be animalcules, and were accepted as such until the middle 

 of the nineteenth century, when F. Cohn classed them as 

 belonging to the vegetable kingdom, and listed them among 

 the fungi, making of them the third variety of fungi, the 

 schizomycetes or cleft fungi ; the other two being the saccharo- 

 mycetes or sprouting fungi (the yeast plant), and the hyphomy- 

 cetes or mucorini (the moulds). 



THE CLASSIFICATION OF COHN FOR BACTERIA. 



This, as just given, is accepted to-day by all authori- 

 ties, though it is open to criticism. Although it is true that 

 the great majority of these organisms like the fungi possess 



