POWDERED VEGETABLE DRUGS 



globes filled with water appeared magnified, but this phenomenon was 

 attributed to the water, which leads to the conclusion that glass lenses 

 were unknown even after glass was in use. 



The first simple microscope of which there is any authentic record 

 was made about 1300 and was known as vitrum pulicarium (flea glass). 

 It consisted of a shtirt cylindrical tube, at the upper end of which the 

 lens was placed. The lower end carried two pieces of glass, just in 

 focus, between which the object was held. The object to be inspected 

 or marveled at was usually a flea, hence the name. The so-called 



x ^ "seed microscope" was similarly constructed. 



The sides of the tube were open for the admis- 

 sion of light and the two glass plates at the 

 lower end contained small seeds. These first 

 simple microscopes were mere toys and no scien- 

 tific use was made of thenu 



It was not until about the year 1650 that 

 scientists began to make use of the simple micro- 

 scope. Their possible value in scientific investiga- 

 tions being recognized, special efforts were made to 

 increase the magnifying power of the instruments 

 as well as their definition. 



Pere della Torre, of Naples (1776), andLebaillif 

 made exceUent glass globules with very high mag- 

 nifying power. Ch. Chevalier in his treatise on 

 FIG. 1. Leeuwen- the microscope describes the conditions and re- 

 hoek's simple micro- quirements for making good magnifying globules, 

 scope (1670). He gtated that the g^bules must have a perfectly 



a, lens; b, adjust- spherical form, that the glass must be pure and 

 mentjc, object-holder: , i c r u uui 



' entirely free from air bubbles. 

 a, metal plate. 



The Dutch scientist, Anton van Leeuwenhoek, 



used highly perfected lenses with mechanical conveniences for focus- 

 sing the object under examination. In 1677 he discovered a large 

 number of fresh water animalculae as rotifers, vorticellse, etc. In 

 1673 he discovered the red blood corpuscles, which, he said, measured 

 Mg40 of an inch. The diameter, as determined by the most perfect 

 modern instruments, is ^200 of an inch; the difference being due to 

 the spherical aberration of these early magnifiers a source of error 

 then not fully understood. Stellati, the Italian scientist, employed 

 excellent lenses in his study of the anatomy of the bee (1685). 



In 1740 Wilson improved the effectiveness and convenience of the 

 simple microscope by supplying a stationary stand with foot and an 

 adjustable mirror for illuminating by transmitted light. 



