E. M. JOPE 



pictures of the cell absorption at any one time. Our system, of course, 

 requires microscopic equipment with a considerable degree of achro- 

 matism. We have found in practice that it is possible to choose glass 

 condensers and objectives which are sufficiently achromatic over the 

 wavelength region of the Soret band (e.g. 370-440 m|j.) to give at any 

 rate preliminary results of some value. Further down in the ultra- 

 violet, however, the dispersion of quartz changes much more rapidly 

 with wavelength than does that of glass in this region; even quartz- 

 fluorite ' achromats ' have at optimum wavelength a range of only 

 about 15m}j. over which their focussing remains adequately constant 25 . 

 More recently it has been possible to overcome this difficulty by using 

 in collaboration with Dr R. Barer (Department of Human Anatomy, 

 Oxford), a reflecting microscope 26 ' 27 which is of course completely 

 achromatic, made by Dr C. R. Burch of Bristol University. This 

 instrument has an aspherical large mirror and spherical small one, 

 and the condenser we used was a replica of the objective : this system 

 gives a numerical aperture of 0-65. The reflecting surfaces were 

 aluminized. 



Two complementary systems have been used by us for spectral 

 analysis of the image of the cell structures given by the microscope 

 illuminated from a continuous source. In the first the moving plate 

 method 21 ' 22 was used to record the spectrogram of a small portion of 

 the image of the cell structure isolated by a short spectrograph slit, a 

 system analogous to the standard spectroscopic eyepiece. By this means 

 we have shown up the Soret band in the cytoplasm of individual 

 human red cells and shown up also the existence of the extra band 

 at 378 my. observed earlier by the suspension methods. This technique 

 is particularly adapted to the revealing of such finer gradations in 

 spectral absorption 28 ' 30 . 



Spectrogram 



/mo 9 e of f" ' ' " [..v/v/ va.:., y£^j -^ Control Beam Figure 10. Diagram of image 



cm trom — ~(m\~ — Nucleus m from microscope projected on to 



Microscope T' teliiM C Cytoplasm s ftt of spectrograph and resulting 



\ Control Beam * 



Spectrograph S//A Wavelength—^ Spectrogram. 



In the second system the image from the microscope was again 

 focussed on the spectrograph slit, and as this slit is in focus on the 

 spectrograph plate a spectrogram was obtained of the cross-sections of 

 the cell-structure transmitted by the slit (Figure 10). Figure 11 shows 

 a spectrogram of a cross-section across a frog red blood cell in the 

 Soret band region, produced by this technique using the reflecting 

 microscope and an overrun tungsten filament lamp : the Soret band 



214 



