422 SUMMARY OF CURRENT RESEARCHES RELATING TO 



convenient distance, are pivoted two spring fingers. The machine is 

 slipped over the anterior edge of the stage, the cnrved spring firmly 

 presses the right edge of the stage, while the two spring fingers grip its 

 left edge and under surface. This construction is sufficient to hold the 

 machine immovably on the stage, and is adapted to engage stages of 

 different widths within the limits of stage sizes usually employed with 

 Microscopes. 



(5) Microscopical Optics and Manipulation. 



Spirochaeta pallida.* — -E. M. Nelson shows a rough sketch (fig. 3()) 

 of Spirochaeta pti/Iida made under a power of 4000 diameters, which 

 illustrates two details hitherto unknown. They are (1) the long whip- 

 like flagella, and (2) the beaded structure of the organism. The length 

 of the organism is ttjVo? the width of the helix about aoioTr^ the pitch 

 of the screw about jrhsv^ the length of the flagellum about ^xiVu? ^^^ 

 the thickness of the thread of the body ^s-qths ^^- The longest of the 

 organisms measured tbVtt i'^-) ^^^^ the shortest was somewhat less than 

 half that size. The pitch of the screw is very variable. The thickness 



I I I I I I 



Fig. 30.— Scale, ^-^ in. by 4000. 



of the thread of the body was corrected for antipoint. The organism 

 does not resemble a spiral, but is like a helical screw. The helix of the 

 one drawn was measured both by a screw micrometer and by the simpler 

 method of extinction ; the results were identical. The flagellum is a 

 fine but not a difficult microscopical image, but the visibility requires 

 most careful microscopical work. The image of these was so difficult 

 that it was found impossible to step them with the web of the micro- 

 meter. As a rough estimate they may be 110,000 to the in. 



Immersion fiuid.f — E. M. Nelson writes that microscopists should 

 know that it is now almost impossible to procure proper immersion oil 

 for Microscope object-glasses. A proper fluid was invented by Abbe, 

 and was sold by the firms of Winkel and Zeiss. The " cedar oil," as 

 commonly sold, and also the immersion fluid of Lectz, have not the 

 requisite optical properties, therefore objectives immersed in them do 

 not yield their best results. The following formula gives Abbe's latest 

 results. The ingredients are three, viz. : (1) White oily tacamaque of 

 Guibourt ; (2) oil of cedar {Juniperus vircjiniand) ; (3) castor oil. The 

 proportions are 29 grammes of tacamaque dissolved in 22 c.cm. of cedar 

 oil, to which are added 14 c.cm. of castor oil. 



* English Mechanic, June 2, 1916, p. 371 (1 fig.), 

 t English Mechanic, June 2, 1916, pp. 370-1. 



