THE DEVELOPMENT 5 



Development of the Microscope. — Microorganisms, and 

 bacteria in particular, are exceedingly minute. Individual 

 cells cannot be seen with the naked eye, and very few 

 observations can be made satisfactorily without the aid of 

 a compound microscope. It is apparent, therefore, that 

 little could be learned concerning bacteria until the micro- 

 scope had been highly perfected. 



Apparently the first authentic record and description of 

 bacteria is that by a Dutch lens maker named van Leeu- 

 wenhoek. This investigator succeeded in so combining 

 lenses as to secure magnifications greater than those of his 

 predecessors. In a letter written in 1683 to the Royal 

 Society of London he commented at some length upon his 

 microscopic observations of tartar from teeth and of various 

 decaying materials. Accompanying his paper were draw- 

 ings of the minute organisms which he observed. These 

 were published in the proceedings of the society, and con- 

 stitute the first pictures of microorganisms. His observa- 

 tions and pictures are sufficiently accurate so that one 

 familiar with the microorganisms of the mouth can recog- 

 nize and identify at least some of the forms illustrated 

 with a high degree of probability. 



During the next hundred years lenses were improved and 

 compound microscopes came into common use. In 1783 

 a Danish investigator, Miiller, published a study of micro- 

 organisms which were observed in various decaying mate- 

 rials and in water. He worked out the first scientific 

 classification of these lower forms of life. Undoubtedly 

 some of the organisms observed were bacteria, and it is 

 to Miiller that we owe certain of the common names used 

 in bacteriology, such as vibrio and bacillus. 



During the next half century the microscope was still 

 further perfected. Ehrenberg in 1836 greatly elaborated 

 and improved the classification and observations of Miiller. 

 A few years later the principle of the oil immersion -lens 



