260-m// region of the ultraviolet spectrum makes possible the identifica- 

 tion and measurement of these substances in cell structures such as the 

 chromosomes and cytoplasm (Figure 11-18). 



The most serious drawback to use of the ultraviolet microscope is the 

 lethal effect of ultraviolet radiation on living cells. The amount of radi- 



Cy toplasmic 

 Nucleic acid % 

 5 



Hemoglobin 10" fiq 



Phase 



Stem cell 



Mature eel 



Figure 11-20. Graph Showing Changes in Cytoplasmic Composition Dur- 

 ing Mammalian Red Blood Cell Formation as Measured by Ultraviolet Mi- 

 crospectrophotometry. Synthesis of RNA associated with endocellular growth 

 processes is completed before formation of the mature erythrocyte. The de- 

 velopmental phase where the concentration of cytoplasmic RNA is virtually 

 zero, represents the period during which intensive production of hemoglobin 

 is initiated. Solid circles, per cent cytoplasmic RNA; line through open cir- 

 cles, total amount of hemoglobin in cell; dotted line, total cellular protein. 

 (From Thorell, B., 1947. "The Relation of Nucleic Acids to the Formation 

 and DifTerentiation of Cellular Proteins," Cold Spring Harbor Symposia 

 Quant. Biol., 12, Fig. 14, p. 253.) 



ation necessary to photograph cell structures with ultraviolet light is very 

 close to doses which either kill or seriously damage the living cell. This 

 disadvantage has been overcome somewhat by the use of more sensitive 

 recording devices such as the quartz window television tube. While the 

 advent of television electronics is quite recent in biology it has interesting 

 possibilities for teaching and research. 



240 / CHAPTER 11 



