204 RADIATION BIOLOGY 



"cytochemistry," and in this chapter an attempt will be made to describe 

 and to evalnate critically some of the approaches to this problem of chem- 

 ical organization of the cell. 



2. LAWS OF ABSORPTION 



Since cytological stndies are necessarily carried out at high magnifica- 

 tion with a compound microscope the preparation, a section or smear of 

 an organ, is always examined by transmitted light. For this reason the 



Fig. 6-1. Diagram of the structural features of a serous glandular cell at an early stage 

 in restitution of the secretory granules, c, centriole; mg, mature zymogenic granule; 

 ig, immature zymogenic granule; n, nvideus with masses of chromatin and a large 

 spherical nucleolus; m, mitochondrion. 



technique of cytological microscopy is readilj^ adapted to photometric 

 chemical analysis, in which the nature and amount of material may be 

 determined from the spectral characteristics and intensity of the light 

 which emerges from a semitransparent mass. This fraction of the light 

 is said to be "transmitted"; that portion which entered the object 

 but did not emerge is said to have been "absorbed." Application oi 

 laws of absorption (see Chap. 5, this volume) not only make it possi- 

 ble to use on slides qualitative and (juantitative methods of chemi- 

 cal analysis, but these laws also apply directly to the visual examination 

 of cells since the visibility of a natural or artificial color in a cell depends 

 on whether the colored object absorbs enough light to make it distin- 

 guishable from the surrounding nonal^sorhing regions. 



