ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



367 



uncemented chromium glass and Mint glass, and is embedded in a water 

 reservoir through which a current constantly circulates. 



Fig. -17 shows the complete installation. A small chamber containing 

 a prism is placed over the tube, thus affording direct observation down- 

 wards and photographic observation laterally. In order to get sharp 

 images one of the nicols has an arrangement for the insertion of a red 

 or orange disk to act as a filter. 



KS 



Fig. 47. 



For observations in a gas atmosphere a gas current is made to cir- 

 culate through the interior of the stove, the top being shut down with a 

 quartz glass plate. 



(3) Illuminating- and other Apparatus. 



Dark-field Illumination and Ultramicroscopy in Biology and in 

 Medicine.* — N. Gaidukov's treatise under the above title gives what 

 appears to be a very complete account of the present state of ultra- 

 ruicroscopy. It contains 74 pages of text, 9 pages of bibliography, 

 and 5 plates with descriptive notes. There is also a preface in which 

 the author reminds us that Ultramicroscopy has not been recognised as 

 a distinct branch of science for more than seven years. The work 



* Dunkelfeldbeleucbtung und Ultramikroskopie in der Biologie mid in der 

 Medizin. Von N. Gaidukov. Mit 13 Abbildungen im text, 3 Licbtdruck-und 

 2 Cbromolitbograpbiscben Tafeln. Publisbed by G. Fiscber, Jena, 1910. 



