PHYSICAL METABOLISM 237 



the new connections may be brought about by the 

 electro-magnetic "pulses" or ultra-violet disturb- 

 ances resulting from the impacts, or rather from 

 the sudden stoppage, of the cathode rays on the 

 surface of the body — for this complex of thin 

 pulses, resolvable as they are into waves of very 

 short wave-lengths, corresponding to periods much 

 higher than those of the ultra-violet in the solar 

 spectrum, may set up chemical action, as is well 

 known from the effect of Eontgen rays on photo- 

 graphic plates ; whilst the actual emission of light 

 can be attributed to the breaking down of the 

 molecules thus formed, which is greatly increased, 

 as we shall see, by the presence of free corpuscles, 

 that increase the rate of disintegration. In passing, 

 then, from this to other but allied points, it may 

 be remarked that if the phosphorescent light were 

 due to forced disturbance, its spectrum in the after- 

 glow would differ from that during the time of 

 excitation ; in one case the vibrations being free 

 and in the other forced. Such a difference has 

 never been observed, and the spectrum remains 

 roughly the same under various modes of excitation. 



The Change of Absorption during Fluorescence. 



The independence of the fluorescent periods, 

 however, does not prove that these are due to 

 new atomic connections, or that there are new 

 periods which do not exist when the body is in- 

 active. These modes of vibration may be per- 



