A CRITIQUE OF CYTOCHEMICAL METHODS 



205 



Fig. 6-2. A series of photomicrographs of pancreatic glandular cells, showing structure 

 and the results of various techniques of localization of nucleic acids and proteins. 

 (A) phase contrast, no stain or reaction; (B) Millon reaction for total protein; (C) 

 nucleic acids stained specifically by basic dye, azure A; (D) ultraviolet photograph 

 (254 m/u) showing absorption in regions of nucleic acid concentration; (E) digested 

 with ribonuclease before staining with azure A [compare with (C)]; (F) Feulgen's 

 nucieal reaction for deoxypentose. {Pollister et al., 1951.) 



Inferences from the more general laws of relation of mass to absorption 

 of radiant energy are conveniently summarized by some simple equations, 

 in which the following symbols are used: 



/o = light intensity (galvanometer reading) when no absorbing 

 object is in the optical path (in cytological measurements, the 

 reading through an empty part of the slide) ; 

 Ix = intensity when the absorbing object or sample is in the optical 

 pathway (in cytological measurements, the reading through 

 the cell component) ; 

 T = transmission, h/h (7c T = \00T); 



