256 



PROGRESS IN MICROSCOPY 



absorbance variations of the nucleus versus the wave-length and the 

 curve Cy those of the cytoplasm variations. Cytoplasm absorption 

 at approximately 0-415// correlates the characteristic spectral ab- 

 sorption region of haemoglobin (Soret) which is known by macro- 

 spectrophotometric means. Absorption of the nucleus at approxi- 

 mately 0260 fi is due to nucleic acid. 



In quantitative microspectrophotometric determinations the purpose 

 is to define the concentration of a given substance in the investigated 



KiG. !0.13. The absorption measurement is effected for instance along the line OX 



in the image of the cell. 



. 05 - 



Fig. 10.14. Absorption variation versus the wave-length (after Barer, Holiday and Jopes): 

 Curve N, absorbance variations of the nucleus; Curve Cy, absorbance variations of the 



cytoplasm. 



object. Determinations may be either absolute or relative when com- 

 paring the concentration of the substance in two difterent elements 

 of the specimen. 



Let us assume that microspectrophotometric measurements evince, 

 in the investigated object, the absorbance d, at the wave-length /. 

 Let / be the thickness of the object (in cm), C the concentration of 

 the substance within the object (in grammes per litre) and K the 

 absorptivity (extinction coefficient) of the substance at a given wave- 



