CYTOCHEMICAL TECHNIQUES FOR NUCLEIC ACIDS 



85 





250 



300 350 



Wavelength 



Fig. 7. Left: Ultraviolet absorption curves. A. Telophase spindle from lily ovary 

 wall, acetic alcohol -fixed, 5-/x section, mounted in zinc chloride-glycerin. B. Cyto- 

 plasm, Drosophila salivary gland cell, smeared and mounted in 50% acetic acid with 

 1.25% lanthanum acetate as suggested by Caspersson.'" C. Nucleolus of same cell. D. 

 Nuclear sap from late salamander (Triturus) oocyte, acetic alcohol-fixed, cut at 5 /x 

 and mounted in zinc chloride-glycerine. Right: The effects of mounting media. Egg 

 albumen, heat-denatured and fixed in formalin, cut at 5 fi. A. Mounted in glycerin. 

 B. Mounted in chloral hydrate-glycerin. Curve A — B demonstrates the amount of 

 light lost through scattering; an increased scatter in the region of maximum absorp- 

 tion is evident. The section was first mounted in chloral hydrate-glycerin for curve B. 

 The moiinting medium was then removed with absolute alcohol (1 hour), the section 

 remounted in glycerin, and the same area was remeasured. Some swelling of the albu- 

 min may have occurred in the chloral hydrate-glycerin. 



ultraviolet irradiation.^*'* In some cases this may involve actual destruction 

 of pyrimidine rings. ^^^ The effect may be reduced in frozen-dried tissue 

 sections if lanthanum is added to the mounting medium.^** 



Since protein absorption broadly overlaps that of the nucleic acid com- 

 ponent, changes in the shape of protein curves are also important for 

 nucleic acid estimation. The tyrosine peak at higher pH levels (above 10) 

 shifts to about 290 m/x and increases in height.'^"' A similar shift, originally 

 attributed to the influence of basic proteins, occurs in some tissues ;i*^ since 

 basic proteins do not show the shift, '^^ however, other factors as yet un- 



1" H. K. Catchpole and I. Gersh, Discussions Faraday Soc. 9, 471 (1950). 



185 D. Rapport and A. Canzanelli, Science 112, 469 (1950). 



i8« W. Stenstrom and J. Reinhard, J. Phys. Chem. 29, 1477 (1925). 



1" T. Caspersson, Chromosoma 1, 562 (1940). 



188 A. E. Mirsky and A. W. Pollister, J. Gen. Physiol. 30, 117 (1946). 



