THE USE OF SOLUBLE PRUSSIAN BLUE 735 



and from these regions of active metabolism, are not the seats 

 of interchanges between their contents and the tissues. 



As might be expected, very little reducing power can be 

 demonstrated by the method of immersing even the most active 

 tissues in warm Prussian blue and gelatine, for only the cells 

 at the surface of the solid piece of tissue (liver, kidney, gland) 

 exert any reducing power, and thus produce a greenish appear- 

 ance only in their immediate neighbourhood. 



This method is vastly inferior to that of perfusing the sub- 

 stance to be reduced : by perfusion through the capillaries every 

 cell-district equally throughout the cell-mass has the reducible 

 material brought within the sphere of biochemical activity. 



This point needs no further elaboration ; but it must be 

 borne in mind by subsequent workers with this Prussian blue 

 method. Living tissue cannot be expected to act like so much 

 pyrogallol, for instance, which, dropped into a solution of 

 Prussian blue, reduces it with extreme rapidity; a piece of 

 living liver not being distributed throughout the liquid medium 

 cannot be expected to act like the liquid-reducer. 



In one or two experiments on perfusion of kidney (lamb) I 

 used wsoluble Prussian blue (Williamson's blue) in tap-water 

 suspension (or " colloidal solution ") ; no flow through the ureter 

 was obtained, and a very much less perfect degree of reduction 

 in the capillaries. I regard it as quite unsuitable for reduction 

 experiments owing to its insolubility preventing its passage 

 through vascular endothelium in order to come within the 

 sphere of the reducing power of the living epithelial cells. 



In investigating the reducing power of an organ or in 

 attempting to assign to a given organ its relative position in 

 the scale of energy of reduction, one must avoid the fallacy of 

 overloading a poisoned organ with injection-mass. For instance, 

 in the case of the lungs, it would be incorrect to say that 

 because the lungs are found filled with a perfectly blue mass 

 after having been perfused for half an hour or so, they have 

 no power of reduction. 



As living protoplasm, pulmonary tissue has certainly some 

 reducing power ; but this is exerted in the earliest stages of 

 the perfusion and, the protoplasm being shortly thereafter 

 poisoned, no subsequent Prussian blue is reduced, and so we 

 end with the lungs poisoned and overloaded with the unaltered 

 blue ferric salt. 



