CIRCULATING SYSTEM. 347 
and VauqueE in regarded it in the state of a sub-phosphate, 
and as giving colour to red blood. This opinion was, for 
a considerable time, servilely embraced by chemists, but is 
now as generally abandoned. It was first successfully at- 
tacked by Dr WE ts, in his ‘‘ Observations and Experi- 
ments on the Colour of Blood *.” Subsequent experiment- 
ers have fully confirmed his views, particularly Brrze- 
Lius +, Branpe, and latterly Vavevetin{, and have 
greatly extended our knowledge of the habitudes of this 
substance with acids and alkalis. Mr Branpr has even 
succeeded in dying cloth with it, but he found consider- 
able difficulty in fixing the colour. The most effectual 
mordants he discovered, were the nitrate and oxymuriate 
of mercury §. No experiments have hitherto been per- 
formed on the colouring matter, or mechanical or chemical 

* As his remarks have not attracted the attention they deserve, I shall 
here state his arguments in his own words :— 
‘¢ J. I know of no colour, arising from a metal, which can be perma- 
nently destroyed by exposing its subject, in a close vessel, to a heat less than 
boiling water. But this happens with respect to the colour of the blood. 
“ 2. If the colour from a metal, in any substance, be destroyed by an al- 
kali, it may be restored by the immediate addition of an acid ; and the like 
will happen from the addition of a proper quantity of alkali, if the colour 
has been destroyed by an acid. The colour of the blood, on the contrary, 
when once destroyed, either by an acid or an alkali, can never be brought 
back. 
«¢ 3. If iron be the cause of the red colour in blood, it must exist there 
in a saline state, since the red matter is soluble in water. The substances, 
therefore, which detect almost the smallest quantity of iron in such a state, 
ought likewise to demonstrate its presence in blood; but, upon adding Prus- 
sian alkali, and an infusion of galls, to a very saturate solution of the red 
matter, I could not observe, in the former case, the slightest blue precipi- 
tate; or, in the latter, that the mixture had acquired the least blue or pur- 
ple tint.”—-Phil. Trans. vol, 1xxxvii, p. 429. 
+ Annals of Phil. vol. ii. p. 24. + Ib. vol. vii. p. 230. 
§ Phil. Trans. 102, p. 110. 
