85 



stituents had the same effect with the other two substances. Tissue 

 extracts were found to produce a long-lived excitation with in 

 quinidine at a ver)- high dilution. 



There is one conclusion we can draw from this for our later ex- 

 periments. When studying the question how far £* is involved in 

 biological action and how far the modifications of this £* can 

 explain drug or hormonal action, we will have to consider also 

 the lifetime. A drug action may very well consist of modifying 

 the lifetime or modifying the influence of another agent, such as 

 glutathione, on the lifetime of an excitation. 



SUGAR AND ALCOHOLS 



In the experiment described in Chapter 5 the phosphorescent 

 light emission of rhodamin was increased by thiamine. In the 

 present chapter a similar effect was obtained with sodium. We 

 may ask whether such an increased light emission is due to an in- 

 crease or a decrease in the stability of the triplet state.'* These sub- 

 stances may have caused increased light emission by making the 

 triplet less stable and increasing herewith the probability of a 

 return of the excited electron from the triplet into the ground 

 state (Ti -^ G in Fig. 5). It is equally possible that these sub- 

 stances might have increased phosphorescence by rendering the 

 triplet more stable allowing a saturation of the triplet level. The 

 greater the number of the electrons in the triplet state, the greater 

 the probability that some of them will drop back under light emis- 

 sion into the ground state. In this case we could expect that the 

 electrons emit their photon wdth a delay and give signs of a long- 

 lived excitation. A long-lived excitation may declare itself in an 

 afterglow, or in a phosphorescence observable in a slowly moving 

 phosphoroscope. The rhodamin, in presence of thiamine or so- 

 dium showed no such afterglow so that it seems likely that the 

 increased light emission was due in this case to i reduced stability, 

 or at least to an increased probability of the Ti ^ G transition. 



Several instances were quoted on the previous pages in which 



