2 6o HAEMOGLOBIN. 



chloric or sulphuric acids, exhibits 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 denned 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- 

 bands, 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 ha j matoporphyrin has 

 given me the following results : l Acid solutions of hamiatoporphyrin, 

 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 hamiatoporphyrin 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. Garrod), 

 and in larger quantities in certain toxic conditions, especially in one of the 

 forms of chronic sulphonal poisoning. 



H^MATOIDIN. 



This name was applied by Virchow 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). 

 Hiematoidin, 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 hsematoidin 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 011 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. Roy. Soc. London, 1896, vol. lix. p. 279. 



2 MacMunn, Journ. PhysioL, Cambridge and London, 1885, vol. vii. p. 240; vol. 

 viii. p. 384. 



