1150 



hj'drochloric acid is added (o it, so that the whole mass contains the 

 colloidal substance. 



Now if the lattei- is sensitive to photoelectricity, the silicic acid 

 disc has become so too, either oiilj superficially if prepared on the 

 first method, or Ihroughont, if [)repared b}' the 2"^- method. 



in this manner we found with the following physiological substances: 



Lighted Not lighted 



Silicic acid disc -|- serum-albumin (weak sol.) 9 miu. J 8 n\\n. 



„ -\- serum-globulin ,, ,, 



„ -f" lecithin sol. (sat.) 



,, -(- horse's blood 



,, -|- Casein sol. (sat.) 



„ -|~ Pancreatin 2 "/, 



,, -|- lecithin -f- chloroform 



„ -\- sat. fresh aq. nuclein sol. 



,, -f~ ^'^^- l'"6sh tyrosin sol. 



If the gel, just described, is saturated with a ci-ystalloid solution, 

 not a vestige of photo-electricity is noticeable. 



Converted beforehand to the colloidal state the molecules are 

 apparently spread as a continued layer on and in the gel in order 

 to furnish the violet light with an adequate point of application for 

 its photo-electrical action. 



When the thickness of the silicic acid gel is made to be al)Out 

 2 or 3 m.m. and the colloidal solution is poured out over the surface 

 turned towards the light, a weak photo-electricity will be observed 

 also on the surface that is turned away from the light, apparently because 

 the slow electrons, swarming from the light, are strong enough to 

 penetrate through the gel. When, howevei', the colloidal solution is 

 poured out over the surface turned away from the light, the hindmost 

 layer remains insensitive, as the light cannot I'each it. It is checked 

 by the silicic acid. Neither water nor glycerin check the light 

 appreciably in such thin layers. 



By addition of eosin we have endeavoured to utilize the light that 

 penetrates, however without success for photo-electricity, which is 

 not surprising since visible light is not generally capable of arousing 

 photo-electricity (except in alkali-metals, and cleansed aln minium, 

 magnesium and zinc). 



The object of our gel-experiments has been to procure a model of 

 an animal tissue, with which we might be able to perform typical 

 experiments on the action of light. The silicic acid gel is particularly 

 adapted for this purpose, as, contrary to the gelatin- and agar-gels, 



