USE OF CHROMOGENIC REAGENTS 



99 



degree in the visible. An exception to this is the very interesting 

 study which Thorell (1947) has made of the formation of hemo- 

 globin during the development of red blood cells. 



A typical example of the work of Caspersson is illustrated by 

 Fig. 5. 



1.0 



2200 2400 2600 2800 



A.U. 



3000 



3200 



Fig. 5. Extinction coefficients for a point on a chromosome (upper curve) 



and in the cytoplasm (lower curve) of a Tradescantia pollen mother cell. 



The absorption at 2800 A.U. is mainly caused by protein, and at 2600 A.U., 



mainly by nucleic acid. After Caspersson, 1950, page 66. 



General Principles Involved in the Use of 

 Chromogenic Reagents 



There are a wide variety of agents which may be used in order 

 to produce an absorption of light by proteins or nucleic acids in 

 various parts of the spectrum. Up to the present these agents 

 have been almost entirely restricted to the development of ab- 

 sorption bands in the visible region of the spectrum. It seems 

 likely that in the future attempts will be made to use reagents 



