114 
Mr. W. Brande’s Chemical Researches , &c. 
afforded an excellent opportunity of corroborating the facts 
respecting this principle, which have been detailed in the pre- 
ceding pages. Although I could detect no traces of iron, by 
the usual modes of analysis, minute portions of that metal 
may, and probably do exist in it, as well as in the other 
animal fluids which I have examined ; but the abundance of 
colouring matter in this secretion should have afforded a pro- 
portional quantity of iron, did any connection exist between 
them. It has been observed that the artificial solutions of the 
colouring matter of the blood, invariably exhibit a green tint 
when viewed by transmitted light : this peculiarity is remark- 
ably distinct in the menstruous discharge.* 
I hope that some of the facts furnished by the above expe- 
riments, may prove useful to the physiological inquirer: they 
account for the rapid reproduction of perfect blood after very 
copious bleedings, which is quite inexplicable upon that hypo- 
thesis which regards iron as the colouring matter, and may 
perhaps lead to the solution of some hitherto unexplained 
phenomena connected with the function of respiration. There 
can, I think, be little doub'c that the formation of the colouring 
matter of the blood is connected with the removal of a portion 
of carbon and hydrogen from that fluid, and that its various 
tints are dependent upon such modifications of animal matter, 
and not, as some have assumed, upon the different states of 
oxidizement of the iron which it has been supposed to contain. 
* I could discover no globules in this fluid ; and although a very slight degree of 
putrefaction had commenced in it, yet the globules observed in the blood would not 
have been destroyed by so trifling a change. 
