are fluorescein (yellow-green), and rhodamine (orange-red). The ab- 

 sorption and emission spectrum of fluorescein is shown in Figure 11-27. 

 An interesting application of fluorochrome dyes is the fluorescent-anti- 

 body technique in which antibody molecules are combined with a fluoro- 

 chrome. Since the specificity of the antibody for antigen is not destroyed 

 as the result of its combination with the fluorochrome, it is possible to 

 stain appropriately prepared sections of living tissue with fluorescent 

 antibody to determine sites of antigen formation. By illuminating the 



Figure 11-28. Immunofluorescent Photomicrograph of Human Amnion 

 Cell from a Culture Infected Eight Days Previously with Measles Virus. Note 

 perinuclear location of one of two prominent cytoplasmic concentrations of 

 virus antigen. (From Rapp, F., Gordon, 1., and Baker, R. F., 1960. "Observa- 

 tions of Measles Virus Infection of Cultured Human Cells. I. A Study of 

 Development and Spread of Virus Antigen by Means of Immunofluores- 

 cence," J. Biophys. Biochem. CytoL, 7, Fig. 2, Plate 17. Courtesy of Dr. Fred 

 Rapp, Philip D. Wilson Research Foundation, New York, N. Y.) 



tissue with ultraviolet light, one can observe microscopically the sites 

 where specific antigen is formed by the fluorescence emitted from the 

 antigen-antibody-fluorochrome complex. The antigens of a number of 

 viruses (e.g., poliomyelitis, measles, influenza, mumps, chicken pox) 

 have been localized by this method in tissues of infected animals (Figure 

 11-28). 



With a few minor changes, the conventional optical microscope can 

 be adapted easily for fluorescence microscopy. Most of the fluorescent 

 substances present in biological materials emit visible light when illumi- 

 nated with the longer- wavelength ultraviolet (about 400 m^). Since 

 optical glass will transmit ultraviolet light down to about 350 m/<, stand- 



250 / CHAPTER 11 



