ULTRAFILTER 



364 



ULTRAVIOLET MICROSCOPE 



research. Efforts to improve the ultra- 

 centrifuge are continuing. Beams J. 

 Wash. Acad. Sci., 1947, 37, 221 has de- 

 scribed a magnetically supported and 

 magnetically driven ultracentrifuge. 

 This machine in experimental tests 

 obtained rotational speeds of 48 million 

 R. P. M., thus producing a centrifugal 

 force of 500 million times gravity. 

 Further development of the ultra- 

 centrifuge will undoubtedly lead to a 

 wider application and more refined tech- 

 niques for researchers interested in 

 problems involving sedimentation and 

 fractionation of mixtures. See Cen- 

 trifugation. 



Ultrafilter. For filtering small volumes of 

 fluid the ultrafilter of Johnson, H. C. 

 and Kirk, P. L., Mikrochemie ver. 

 Mikrochim, Acta, 1940, 28, 254-257 is 

 recommended by Glick, p. 487. See 

 easily constructed apparatus described 

 by Clark, L. C, J. Lab. & Clin. Med., 

 1951,37,481-484. 



Ultramarine Green, an exogenous pigment, 

 a sodium aluminum silicate and sulfide 

 (Lillie, p. 138). 



Ultramicroscope, see Darkfield. 



Ultrasonic Vibrator. Type used to test 

 effect of ultrasonics on blood elements 

 by Morrow, P. L., Bierman, H. R. and 

 Jenkins, R., J. Nat. Cancer Inst., 1950, 

 10, 843-859. 



Ultrasonics. The division of acoustics com- 

 prising sound frequencies beyond the 

 limits of perception by the human ear. 

 Radiation of this sort can be very de- 

 structive to living cells. The tech- 

 nique and results are well described by 

 Gregg, E. C, Jr. in Glasser's Medical 

 Physics, 1591-1596. 



Ultraviolet Microscope and Color Transla- 

 tion Process. A microscope using 

 ultraviolet radiation instead of or- 

 dinary light to form an image is some- 

 what of a misnomer, for there is nothing 

 to be seen. One must expose a photo- 

 graphic plate sensitive to the ultra- 

 violet rays to record the image. If the 

 ultraviolet is used only to excite 

 fluorescence then of course a visible 

 image is produced as has been described. 

 We are here concerned with images 

 which are not visible. 



In accordance with the law, already 

 mentioned, R = X/2 N. A. increased 

 resolving power can be achieved by 

 employing the shorter wave lengths 

 of the spectrum. Considerable im- 

 provement of the image is obtained by 

 using monochromatic blue light with 

 the ordinary "achromatic" type of 

 objective; but with highly color cor- 

 rected "apochromatic" lenses there is 

 little to be gained by so doing. The 



ultraviolet region of the spectrum of- 

 fers wave lengths as short as 0.15 m, 

 most of which are produced very con- 

 veniently by modern mercury and 

 hydrogen arcs. Therefore, photog- 

 raphy in the ultraviolet should double 

 or even triple the resolving power of 

 a lens if everything else is held constant. 



Since ordinary optical glass is nearly 

 opaque to ultraviolet light lens makers 

 must use natural quartz, or fluorite, 

 components throughout the system. 

 This puts rather severe limitations on 

 the lens designer as it narrows his 

 range of possible corrections. For 

 example, an all-quartz objective must 

 be used with ultraviolet radiation of a 

 specified wave length in order to get a 

 good image (Lavin, G. I., Rev. Sci. 

 Inst., 1943, 14, 375-376). Focus is 

 obtained by trial and error. This 

 makes observation somewhat labori- 

 ous and almost impracticable for living 

 material. Ultraviolet microscopy is, 

 however, used with considerable success 

 in the study of fixed, unstained cells 

 because proteins and nucleic acids 

 show specific absorbtion at 0.280 m 

 and 0.260 ^ respectively (Caspersson, 

 L, J. Roy. Micr. Soc., 1940, 60, 8-25). 

 Thus chromosomes, rich in nucleic acid, 

 reveal themselves in strong contrast 

 and high resolution (Ludford et al., 

 J. Roy. Micr. Soc, 1948, 68, 1-9). 

 After proper calibration one can use 

 the blackening of a plate, or ultraviolet 

 photocell currents, to measure the 

 concentrations of absorbing materials 

 in various structures under examina- 

 tion. 



A remarkable advance in ultraviolet 

 microscopy has recently come about 

 with the development of the color 

 translation rnicroscope (Land, E. H. et 

 al., Science, 1949, 109, 371-374), for 

 which an objective lens corrected for 

 three wave lengths in the ultraviolet 

 has been designed. The operator takes 

 a photograph at each wave length. 

 These negatives show somewhat dif- 

 ferent details because the materila 

 being studied has different ultraviolet 

 absorbing powers at these three wave 

 lengths. The negatives are then 

 treated, as in the conventional process 

 for visual color photography, by as- 

 signing to each negative one of the 

 primary colors. The result is a color 

 print representing in an arbitrary way 

 something which is invisible to the eye. 

 Thus, changes in the ultraviolet ab- 

 sorption spectra of the materials are 

 revealed by changes in the apparent 

 colors of details in the print; hence the 

 term "color translation." 



