PHYSICAL METABOLISM 247 



Merritt have studied the absorption in different 

 parts of the spectrum and have found that it 

 corresponds, as we should expect, to the fluorescent 

 spectrum, being a maximum when the intensity of 

 the fluorescence is also a maximum. Nay, more, 

 the absorption and fluorescence on the whole run 

 parallel, so much so that the one increases with 

 the other, until a maximum is reached, when a 

 saturation efiect occurs, after which the absorption 

 remains constant with further increase in the 

 fluorescence. 



The accompanying figure will make this quite clear. 



The intensity of the fluorescent light would be 

 proportional to the illumination after the absorp- 

 tion has reached a maximum. 



The substances which they worked with were 

 dilute solutions of fluorescein in water, of eosin in 

 alcohol, and resorcin in alcohol, and in every 

 case the change of absorption was most marked. 

 There can be no question but that the change of 

 absorption throws much light upon, and gives us 

 an insight into, the molecular processes which 

 underlie the phenomenon of fluorescence. 



It is not thus, as Stokes supposed, a rousing up 

 of pre-existing modes of vibration, but an actual 

 change in the structure of the body, with new 

 atomic connections, which in being resolved into 

 their original condition radiate intensely, and thus 

 give rise to the luminosity which is observed. 

 Thus the difierence in the absorption of the fluor- 

 escent light is itself due to the temporary change 



