and Laboratory Methods. 



165P 



the table. The part of the patient's body to be pictured is arranged upon the 

 table in proper position over the plate. The tube is then brought into position 

 over the part, and an exposure made. The carrier is then opened, the plate 

 removed, and another inserted. The tube is moved two and one-half inches, 

 and a second exposure made. 



These two plates, when developed, constitute stereoscopic X-ray negatives. 

 They may be viewed at once in a Wheatstone reflecting stereoscope by trans- 

 mitted light, or they rnay be reduced to a size suitable for the refracting stereo- 

 scope, and viewed as positives on glass or paper. 



I wish to acknowledge my indebtedness to Mr. W. F. Folmer, of the Folmer 

 & Schwing Manufacturing Co. of this city, to whose careful oversight the 

 carrying out of the details of construction is due. 

 New York. A. B. JOHNSON. 



NOTES ON THE MICROSCOPE. 



II. Early Accessories. 



A comparison of the earliest accessories with those now in use shows that 

 many of them are almost identical. Many of the old forms have fallen into 

 disuse only to be revived as new from time to time. The concave reflecting 

 mirror, used attached to the objective to illuminate opaque objects, known as 

 Lieberkuhn's illuminator, was first invented by DesCartes in 1637, Lieberkuhn's 

 adaptation dating from 1738, a century later. Both DesCartes and Lieberkuhn 

 mounted a magnifying lens opposite the central opening, and the object was 

 placed in the focus of the mirror. 



Zahn. in 1702, figured a simple mi- 

 croscope with a set of rotating dia- '^^^'^ 

 phragms of various sizes for increasing 

 the efficiency of the lens. Subsequent 

 makers do not seem to have made use 

 of this improvement until about 1820, 

 when it was revived as new by Le 

 Bailiff. 



The very early microscopes were 

 generally provided with sets of acces- 

 sories specially made for them, and in- 

 tended particularly for the examination of special sets of objects. Musschen- 

 broek's microscope (1690) had with it a pair of forceps with delicate points, 

 and a holder for the object carrier, adjustable in any direction by means 

 of two ball and socket joints. The object carriers were metal rods, provided 

 with one or two points, sharp, rounded or clamp like, for insertion into the 

 object, or for holding a transparent object mounted between mica plates. 

 In a little hand microscope by Baker (17-10) we find a contrivance for holding 

 the object identical in construction, and even in shape, with the stage forceps 



Musschenbroek's accessories. 



