114 THE AMERICAN MONTHLY [May, 



compound microscope, the latter giving greater magnification and better 

 definition. With our improved microscopes an object the one-hundredth 

 of an inch in diameter appears a large object ; an object the one-thou- 

 sandth of an inch in diameter maybe dissected, and a parasite the one- 

 fifty-thousandth of an inch is easil}^ detected under the cover-glass, and 

 distinguished from other species by the use of chemical coloring reagents 

 and other expedients. Dr. Goring, of England, who invented tests for 

 the microscope many years ago, was able with his lenses to get the lines 

 of podura with wonderful perfection. Dr. Royston-Figott wrote, in 

 1S76, that when he was a young medical student it used to be thought 

 the highest point of microscopical skill to be able to take a little diatom, 

 the hippocatnp7^s^ and with a ray of oblique light get its transverse lines, 

 which, on turning the light the other way, disappeared and were replaced 

 by other lines running in a longitudinal direction. 



In 1845 the diatom hippocampus was viewed as a line object and the 

 lenses capable of showing these lines were highly approved. Then there 

 was a contention that they were not lines but series of hexagons, and 

 the late Col. Woodward, who, by using the blue rays alone, was able 

 to photograph the most delicate appearances of microscopic objects, 

 succeeded in resolving the so-called lines of hippocampus into what 

 appeared to be series of spherules or beads. The next photograph 

 obtained by Col. Woodward was the very difficult one of ang-ulatum, 

 the lines of which it was believed he also resolved into beads. 



The members of our society will doubtless recollect that, about a year 

 ago, i\\G Jouffial of the Royal ATicroscopical Society in its summary 

 of current researches relating to microscopy had the following: 



''At the March meeting of the society a photograph by Dr. Van 

 Heurck (director of the Jardin Botanique, Antwerp) was exhibited of 

 P. ang'ulatum., produced with Zeiss's apochromatic objective of 1.63 

 N. A. The note accompanying the photograph was as follows: '1 

 have the honor to submit to the Royaf Microscopical Society a photo- 

 graph of P. angulatum made with the objective of 1.63 N. A., using 

 strictly axial illumination. The fracture of the upper edge shows clearly 

 that the 'beads' are holes in the intermediate layer, and that the form 

 of these holes (beads) is hexagonal, as maintained by Mr. Smith and 

 myself. The form of the small i^ar on the exti'eme top, which is the part 

 of the negative focused, shows that the 'beads' can not be round.'" 



The next stage of advance in the microscope was to resolve the podura 

 scale into little tongues, as it were : and these little marks are still used by 

 opticiansas test objects. This object was most beautifully photographed 

 by Col. Woodward in lines. The next stage in the direction of micro- 

 scopical development was to cut ofT useless rays of light and leave the 

 most useful ones which were found to define the object. 



Drs. Drysdale and Dallinger (names forever noted in the use of the 

 microscope for physiological research) used the highest power (at that 

 time one-fiftieth of an inch) . This is a very delicate objective to use, and 

 the result of their beautiful contrivance was this : they found that in a 

 given field where ordinary powder and an ordinary microscope discovered 

 not the least sign of animal life, even of the minutest form, there were 

 myriads of little monads turning and switching their tails about like 

 long whips under this remarkable power, and it is believed that all con- 

 clusions founded upon the non-appearance of animalcules in a given 



