ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 599 



New Spencer Microscope, No. ii* — This instrument (fig. 36) is 

 intended to be an efficient and comparatively inexpensive type with side 

 fine-adjustment. The arm is large, with a convenient grasp for 

 handling the instrument, and provides a distance of 80 mm. from the 

 arm to the optical axis. The fine-adjustment is of simple type ; the 

 thread-bearing shaft has buttons on both ends and passes back and 

 forth through the arm, carrying with it the free end of the longer arm 

 of a bell-crank lever, the shorter horizontal arm of which raises and 

 lowers the body-tube 0*2 ram. for each complete revolution of the 

 shaft. The vulcanite-covered stage is 112 mm. wide and 108 mm. 

 deep, and is provided with a sub-stage of the quick-screw type ; the 

 upper iris diaphragm is automatically locked open when the condenser 

 is put into place. 



(3) Illuminating' and other Apparatus. 



Improved Apparatus for Dark-ground Illumination in the Early 

 Diagnosis of Syphilis, etc.f — C. H. Mills describes an apparatus 

 (fig. 37) which at the present time meets the need for a really satisfac- 

 tory plant for the detection of ,the Spirochseta pallida in the early 

 diagnosis of syphilis. Now, the most rapid and accurate method of 

 detection is by means of the dark-ground apparatus, but the light which 

 is used with this often fails to give sufficient definition. A good 

 knowledge of optics will, no doubt, enable a comparatively feeble 

 source of illumination to be used with satisfaction, but in routine work 

 we do not desire to practise optics so much as to see the S. pallida. 



With the object of obtaining a thoroughly reliable illuminant, 

 which is easily manipulated and always available without too many 

 preliminaries, the author has for some time been .working upon a 

 design which is now completed and accessible to all, being of British 

 manufacture and at a reasonable price. 



The following are the special features of the apparatus : 1. Extreme 

 compactness and reliability. 2. Always ready for immediate use, and 

 yet, if so desired, can be returned to the cupboard from consulting- 

 room table or laboratory bench without being dissembled. 3. The 

 hand-fed compensating arc lamp requires the minimum of adjustment. 



4. Suitable for use on any existing electric supply — continuous or 

 alternating current — coming within the range of 100-250 volts. 



5. Contact is made from a wall-plug or the bayonet fitting of an 

 ordinary electric lamp. 6. The arc projects a good steady light with 

 ample reserve, rendering differentiation between S. pallida, S. gracilis, 

 S. microdentium accurate, rapid, and comparatively easy. 7. Adapted for 

 any type of Microscope stage. 8. The price is reasonable, and the 

 upkeep, even for constant daily use, inexpensive. The carbons for the 



* Catalogue, Spencer Lens Company, p. 35. 

 t Lancet, October 21, 1916, p. 716. 



