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, that the iron-containing molecular group existing in 

 haemoglobin, upon which its colour, its light-absorbing power, and its 

 capacity to combine with 0, CO, and NO 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 

 of haemoglobin, 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 O'l per cent. vol. of Na(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. 



(&) 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," Arch. d. sc. phys. et nat., 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, tomeii. pp. 340-346. 



4 A. Gamgee, "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 



