ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 765 



in microscopy amongst those who deal with such subjects. It is not 

 generally known, however, that a similar effect can be obtained by the 

 means usually at the disposal of the average microscopist. The author 

 has devised a plan whereby the ordinary Abbe illuminator, if suitably 

 arranged, will do all that is required. There are certain essentials, how- 

 ever, and the first of these is that there must be some centring and 

 focusing arrangements for the condenser. This remark holds good 

 with regard to the new dark-ground illuminators ; and, in fact, the 

 necessity is becoming intensively obvious with the advance of micro- 

 scopical technique. The time will come when every worker will recognize 

 that a centring arrangement to his condenser is of vital importance. 

 The first necessity for the condenser, then, is that a centring arrange- 

 ment must be provided, for the success or failure of the whole attempt 

 is dependent upon accurate centring. A black-patch stop will be used 

 beneath the condenser lenses, and this again must be properly centred. 

 The best way to ensure this is to have a number of disks cut in metal or 

 black paper and fix them to glass disks cut to the size of the stop-carrier 

 of the condenser. The black patch is moved until it is in the right 

 position, and then allowed to dry. The size of the black patch can be 

 ascertained by experiment. It will vary in each case with the numerical 

 aperture of the objective and the condenser. 



The detail in bacteria is not such as calls for a large numerical, 

 aperture in the objective, and the high magnification that is necessary 

 to disclose the contour can be used, while the numerical aperature of the 

 objective can be reduced by a diaphragm at the back. This is the rule 

 that should be followed when using the Abbe illuminator as here 

 described. It is necessary to use, as nearly as possible, a spot of light as 

 the source of illumination. An incandescent gas lamp with a diaphragm 

 in front is probably the best. To test the centring of the whole system 

 the aerial image of the dark-patch stop should be focused when the 

 condenser is in position, and as the condenser is moved downwards out 

 of focus the spot should gradually become reduced in size, maintaining 

 its centre if set axially." 



-tAIDUKOV, N. — Dunkelfeldbeleuchtung und Ultramikroskopie in der Biologie 

 und in der Medizin. 



Jena : G. Fischer (1910) 84 pp. (3 photos., 2 chromolithogr. pis., 



and 13 figs, in text. 



Gambera, M. — Fortschritte auf dem Gebiete mikroskopischer Hilfsapparate im 

 Jahre 1909 



Bamberg: C. C. Buchner's Verlag, 1910 (9 figs.). 

 See also Jahrb. Mikrosk. JaJirg., i. (1909). 



(4 Photomicrography. 



Printing on Sensitized Papers.* — H. Wunderer describes his method 

 of using gas-light photographic papers for the reproduction of diagrams. 

 The diagram is put in a frame with the sensitized paper so that the 

 picture is in contact with the prepared surface. The light travels through 

 the glass plate to the back of the diagram paper, then passes through the 

 paper and through the diagram to the sensitive surface of the paper. 

 The average exposure time is about five seconds. In Breuer's process, 



* ZeLschr. wiss. Mikrosk., xxvii. (1910) pp. 50-1. 



