2 6o HAEMOGLOBIN. 
chloric or sulphuric acids, exhihits in the visible spectrum two absorption- 
bands, of which one, which is the narrower and the weaker, is situated 
between C and D and immediately adjoins D. The second, which is 
much more intense, more sharply defined and broader, lies nearly mid- 
way between D and E ; but nearer the former than the latter. 
Alkaline solutions exhibit in the visible spectrum four absorption- 
1 lands, to wit, a weak band midway between C and D, an equally 
weak band between D and E, but nearer to the former, a more strongly 
marked band nearer to E, and lastly a fourth band, darkest of all, which 
occupies four-fifths of the interval between B and F. 
The spectra of acid and alkaline haematoporphyrin are exhibited in 
Fig. 57. 
A study of the photographic spectrum of hoeniatoporphyrin has 
given me the following results : l — Acid solutions of hsematoporphyrin, 
so dilute as to appear colourless (though presenting, if examined in a 
dark room by means of a beam of sunlight reflected from the mirror of 
the heliostat, the marked red fluorescence previously referred to), exhibit 
an intense absorption-band between h and H. If the solution be 
slightly more concentrated, K is absorbed, and with increasing con- 
centration of the solution the absorption of the ultra-violet extends 
more and more. 
Alkaline solutions of hsematoporphvrin absorb the same spectral 
region, but the intensity of the absorption is greater. 
Haematoporphyrin, as MacMunn has shown, occurs as a colouring matter 
in the integument of some invertebrates and in the egg-shells of certain 
birds. 2 In small quantities it occurs in the normal urine (Arch. G-arrod), 
and in larger quantities in certain toxic conditions, especially in one of the 
forms of chronic sulphonal poisoning. 
H/EMATOIDIN. 
This name was applied by A'irchow to a substance which occurs in 
the form of orange-coloured microscopic crystals (rhombic plates) in old 
extravasations of blood, as in apoplectic clots, and which is certainly de- 
rived from haemoglobin. These crystals are, according to most observers, 
identical in form with those of bilirubin, and when treated with fuming 
nitric acid exhibit the same colour reaction (Gmelin's reaction). 
ILematoidin, like bilirubin, exhibits no definite absorption-band in its 
spectrum, but effects a general absorption of the ultra-violet, violet, and 
blue rays of the spectrum. Opinions were long divided on the question 
of the identity or non-identity of hamiatoidin and bilirubin, but they 
are now generally regarded as identical. 
Certain other substances (of which the chemical history is very imperfect), 
which can be directly obtained by the action of reagents on the blood-colour- 
ing matter, and certain pigments occurring in the organism, and which, on 
grounds more or less satisfactory, have been held to be derived from it like- 
wise, will be considered in the account of the chemistry of the urine as well 
as in that of the chemical processes occurring within the alimentary canal. 
1 Proc. Pay. Soc. London, 1896, vol. lix. p. 279. 
2 MacMunn, Joum. Physiol. , Cambridge and Loudon, 1885, vol. vii. p. 240; vol. 
viii. p. 384. 
