1148 



and, therefore, should iiut be kepi in an uiinosphere laden with 

 odorous matter. 



If, moreover, due care is (aken to keep in all experiments the 

 same distance from tlie source of light to the paper and the same 

 area of the lighted surface of the paper, then the half-way time of 

 the electroscope affords a reliable index for the sensitivity of the 

 liquids. 



The colloidal state is a conditio sine qua non for the photo- 

 electricity of solutions, which will increase with the growth of the 

 micellae, while the solution is still for some time stationary. 



A saturated aqueous solution of engenol e.g. yields: 



Half-way-time. 



For longer periods the sensitivity keeps constant, if there is an 

 excess of engenol. 



In the same waN also various physiological liquids weie examined. 

 This inquiry also showed that : 



1. Crystalloid solutions are not photo-electi-ical. 



2. Colloidal solutions are so, only if they fulfil the above-mentioned 

 three conditions. 



The following materials appeared to be i-esponsive to photo-elec- 

 tricity : 



Half-way-time. 

 Lighted Not lighted 

 Serum-globulin sol. (weak) 

 Serum-albumin sol. (weak) 

 Horse's blood serum 

 Horse's blood 



Horse's blood hemolysed by water 

 Hen's eggwhite in glycerine (sat.) 

 Nnclein (sat. aqueous sol.) 

 It appears then that the sensitivity of physiological solutions is 

 moderate. 



