THE PHOTOGRAPHIC SPECTRUM. 225 
From the extraordinary constancy of this quotient some interesting 
conclusions may be legitimately drawn. (1) The constancy of the 
quotient in all animals affords presumptive evidence, amounting to 
absolute proof, thai the iron-containing molecular group existing in 
luenioglnbin, upon which its colour, its light-absorbing power, and its 
capacity to combine with 0, CO, and XO depend, is identical in 
all animals. The truth of this hypothesis is borne out by many 
weighty facts, e.g. the identity in chemical composition (as revealed 
by analysis) of the iron-containing products of the decomposition 
<>f 1 Hemoglobin, whatever its source; the constancy in the propor- 
tion of and CO which can combine with 1 grm. of haemoglobin 
of different animals. (2) The constancy of the quotient (whether 
solution of crystallised haemoglobin, or an alkaline solution made by 
diluting defibrinated blood with OT per cent. vol. of Xa(OH), or a 
liquid holding intact blood corpuscles in suspension, be investigated), 
shuts out the possibility of more than one colouring matter existing 
in the blood. It renders absolutely untenable the views of Bohr, 
who has assumed the existence of several haemoglobins, possessed 
of different powers of combining with oxygen; and utterly disproves 
Hoppe-Seyler's hypothesis that the colouring matter of the corpuscles 
is distinct from haemoglobin so as to deserve a special designation of 
arterin or phlebin, as the case may be. 
(h) The photographic spectrum. — In the year 1878 the late 
Professor J. L. Soret, of Geneva, in his first memoir on the absorption 
of the ultra-violet rays of the spectrum by diverse organic substances, 1 
announced the fact that diluted blood, when examined with the aid 
of a spectroscope provided with a fluorescent eyepiece, presented in 
the extreme violet, between Frauenhofer's lines G and H, an absorp- 
tion-band which appeared to him to be slightly shifted towards the 
less refrangible end of the spectrum, when the blood solution was 
saturated with carbonic oxide. Soret subsequently 2 confirmed the 
accuracy of the above facts, employing the photographic method in 
his experiments, though he published none of his photographs. Since 
the date of the publication of Soret's short notes on this subject, 
d'Arsonval 3 has independently, and without referring to Soret's observa- 
tions, described anew the extreme violet absorption-band of the blood- 
colouring matter, but without adding to the facts discovered by the 
Swiss observer. 
The complete absence of all reference to Soret's scanty but 
interesting and suggestive observations, in text-books and treatises 
on physiology and physiological chemistry ; and the fact, which my 
own observations soon elicited, that the absorption-band of Soret is 
even more distinctive of the blood-colouring matter than the absorp- 
tion-bands in the visible spectrum which have hitherto engrossed the 
attention of observers, led me to study this absorption-band in more 
detail in haemoglobin, its compounds and principal derivatives. 4 I 
1 J. L. Soret, " Recherches sur 1 'absorption des rayons ultra- violets par diverses 
substances," A rch. d. sc. 'phys. et not., Geneve, 1878, pp. 322, 359. 
2 Soret, ibid., 1883, pp. 194, 195, 204. 
3 A. d'Arsonval, Arch, dephysiol. norm, etpath., Paris, 1890, Ser. 5, tome ii. pp. 340-346. 
4 A. Gamgfe, "On the Absorption of the Extreme Violet and Ultra- Violet Rays of the 
Solar Spectrum by Haemoglobin, its Compounds, and certain of its Derivatives," 
Proc. Roy. Soc. London, 1896, vol. lix. p. 276. 
VOL. I. — 15 
