258 



PROGRESS IN MICROSCOPY 



when it is required to compare the relative contents of the selfsame 

 substance in two different histological structures. Let s^ be the area 

 of the object including the mass Mi of the substance and 5., the area 

 of the other object including the mass Mo of the selfsame substance. 



A =0 435a 



*■% 



0- 



^ X 



Fig. 10.15. Quantity measurement of haemoglobin in a single cell (Thoreil). 



Microspectrophotometric measurements evince absorbance (df)^ for 

 one of the objects and (d^)., for the other. Equation (10.6) allows 

 one to write: 



Ml _ (d^j Si 



(10.8) 



5. CAUSES OF ERRORS IN MICROSPECTROPHOTOMETRY 



The first cause of error is ascribable to stray light, present in all 

 monochromators. The outlet slit lets through, not only the mono- 

 chromatic radiation required but also a continuous background, con- 

 sisting of all the spectrum radiations. This continuous background 



