RECENT ADVANCES IN SCIENCE 545 



as the concentration increases. A rough calculation shows that 

 the energy emitted by an active fluorogene molecule is of the 

 order 10* 12 erg. Photo-electric effects are of the same order of 

 magnitude. 



Supporting the view expressed above, Perrin has observed 

 that the fluorescence of a concentrated solution exposed to light 

 at first increases and then diminishes to zero. This is due to 

 the continuous destruction of the fluorogenes in the chemical 

 sense. As they are decomposed their concentration diminishes, 

 the fluorescent power of each increasing at the same time, 

 with the result that at a certain stage in the decomposition the 

 fluorescence attains a maximum, finally vanishing when all the 

 fluorogene molecules are decomposed. Perrin has not yet 

 examined a sufficiently large quantity of material to determine 

 what this decomposition actually is. 



The next point is to explain how the fluorescent power of 

 a molecule diminishes as the concentration increases. It is 

 evident that contiguity of other molecules affects the fluorescing 

 power of any individual. Perrin makes two suggestions, of 

 which one is that the effect is to be ascribed to a kind of mutual 

 induction or resonance between the molecules when they 

 approach within a certain distance of one another, whereby the 

 energy which is being absorbed in the process of activating a 

 single molecule becomes spread over others, with the result 

 that none of them attains the energy content required. This 

 involves emission of energy in a degraded form, e.g. heat. 

 This aspect of the subject requires further quantitative 

 treatment. 



Finally Perrin has applied his conclusions on fluorescence to 

 the problem of the black spot exhibited by capillary films of 

 great tenuity, and has succeeded in discovering several definite 

 stages or ranges of thickness in such films, any one of which is 

 a whole multiple of an elementary thickness having the ap- 

 proximate value 5 x io -7 cm. 



ORGANIC CHEMISTRY. By P. Haas, D.Sc, Ph.D., St. Mary's 

 Hospital Medical School, London. 



A contribution to the question of the surface action of 

 enzymes is furnished in a recent paper by Bayliss {Arch. Neer- 

 land. Physiol. 191 8, 2, 621); starting from the assumption 

 that the activity of enzymes is due to the absorption upon 



