IN ANIMAL TISSUES. HARRIS. 269 



colloidal complex of albumen and the pigment. There has 

 therefore^ been reduction. Further, this colorless colloidal 

 complex'can be boiled for a short time without its coagulating. 

 For convenience, I call these phenomena, "the Creighton 

 effects". Now there is one significant difference as regards the 

 interaction between proteins and soluble Prussian blue and 

 the interaction between press-juice and that pigment, namely, 

 that whereas there is no fading of the blue in the presence of 

 protein at the end of many hours, the blue in contact with 

 fresh juice fades at once. These are clearly not the same 

 phenomenon; for one thing, in the case of the protein mix- 

 ture the concentration of protein is very much greater than it 

 is in press-juice, but its effect is very much slower. 



Further, if the fading of the pigments is due to protein, 

 then the juice kept for three months, in which the protein is 

 well preserved and is sterile, should reduce as well or almost 

 as well as fresh juice; but this is noticeably not so. 



Again, the rapid falling off in potency as regards reduction 

 within the first day would have no meaning as a phenomenon 

 due to molecular groupings and labile hydrogen, whereas it 

 has a meaning with reference to the deterioration of the bio- 

 chemical activity of a ferment. 



The fact that glycerol extracts of dried liver and of dried 

 kidney possess some reducing power, is more in accord with 

 the conception of that reduction being due to an enzyme than 

 to a protein, for the glycerol extract of dried liver had some 

 cognizable reducing power, and it could have taken up very 

 little protein in "solution". Glycerol by itself has no reducing 

 power. 



Again, glycerol extracts deteriorate in potency with time 

 for which there is no particular reason, if protein be the ac- 

 tive substance. Blood at 40 C does not reduce ferric chloride, 

 but liver-juice at this temperature reduces it to ferrous 

 chloride. There are proteins in both. While giving due weight 

 to Heffter's contentions, and indeed recognizing certain 



