300 On Cutaneous Absorption. 



drawn in different experiments ; they have witnessed 

 the effects of the tests on these portions ; they have 

 compared these effects with those produced by the same 

 tests on different fluids, as water, urine, and diluted se- 

 rum artificially coloured with madder ; and they have 

 unanimously declared the results to be satisfactory and 

 decisive. I think no person of common candour 

 could have witnessed these results without acquiescing 

 in their validity ; indeed scepticism itself must have 

 turned believer, in view of proof so plain. I speak 

 with great confidence on this subject, since I consider it 

 •impossible that so many of my scrutinizing friends, 

 as well as myself, should have been deceived. 



From the effect that the sulphat of iron produces on 

 the red urine, I think it probable that the astringent 

 principle of the madder enters into the circulation, 

 passes the kidneys unaltered, and that the gallic acid 

 it contains seizes upon the oxy-sulphat of iron con- 

 tained in the common sulphat, and produces the brown 

 colour. The reason, doubtless, why the result is not 

 darker coloured, is, that the gallat of iron is very much 

 diluted by the fluid which contains it. The purple hue 

 is probably owing to red particles of madder floating 

 amidst the gallat of iron. I offer no solution of the 

 change produced on an infusion of madder, by means 

 of the vegetable alkali. 



The red particles of the blood, inevitably retained by 

 the serum, and the extremely diluted state of the mad- 

 der it contained, will very well account for the want of 

 eflect produced on the different portions of serum to 



