( 153 ) 



So of the direct natural nerve-stimuli moments only the lig-ht-stimnlns 

 has for the present been (|uantitatively ealculated. Hearing hi mind 

 that the stimulus we found in wlial pi-eeedes to he of the order 

 10~^" ergs, is a minimum stiundus ou a small Held of the retina 

 scarcely measuring 0.002 s(|uai'e millimetres, whereas the total surface 

 coidaining retinal purple is put by König at 700 s(|. nun. ; mor(M»ver 

 bearing in mind that the light of the sun at iMarseilles is estimated 

 by Fabuy ') at 100.000 candles and Ihat tliis enters the eye not 

 under an angle of 23', under which the Hefjier lamp was seen, but 

 from all parts of the tield of view, it will be clear that the light- 

 stimuli of ordinary life can by no means be called innneasurably 

 small. Nor do they act for a single milli-second bul all day long. 

 The energy entering the nervous system in this way will not be a 

 fraction of an erg but a munber of ergs. It is diflicult to make an 

 estimate in this respect as with strong light not the rods but the 

 cones serve as terminal apparatus and in these telenenrons only by 

 analogy a photochemical [)rocess is assumed, which for the rest is 

 unknown to ns. Therefore we inust refrain from such an estimate, 

 l)ut at the same time it seems to us to be iindoubtable that the 

 ner^•ous system receives relatively large quantities of ejiergy in a 

 different ^vay from that by metabolism. 



1, Gompt. Rend. 7 Dec. 1903. 



(August 26, 1904). 



