7 68 CHEMISTR Y OF RESPIRA TION. 
of oxygen for 1 grm. of haemoglobin. The nsual form of haemoglobin is 
y-hsemoglol tin ; this, when dried, gives a crystalline powder, a-haemo- 
globin, which in turn yields, on solution in water, /3-haemoglobin. A 
solution of y-hsemoglobin, when kept in a closed tube, is converted 
into 8-hsemoglobin. These various kinds of haemoglobin have different 
" specific oxygen capacities," by which term Bohr designates the ratio 
between the number of grammes of iron and the number of cubic 
centimetres of oxygen present in a given volume of blood, of blood 
corpuscles or solutions of haemoglobin, saturated with air at ordinary 
pressure and temperature. The red blood corpuscles are said to 
undergo alterations in their specific oxygen capacity during their 
passage through the circulation. 
These results and theories have been subjected to an experimental 
examination by Hiifner, 1 who maintains that in fresh, healthy ox-blood 
there is only one kind of haemoglobin, that the capacity of the fresh 
haemoglobin for carbon monoxide and for oxygen is the same, whether 
it be haemoglobin directly dissolved from red corpuscles or haemoglobin 
first crystallised and then dissolved in water. By experiment, Hiifner 
shows that 1 grm. of haemoglobin takes up T338 c.c. of carbon monoxide 
or oxygen measured at 0° and 760 mm. This is confirmed by the 
following facts. The capacity of haemoglobin to combine with oxygen 
appears to depend upon its iron, one atom of which holds two atoms of 
oxygen. The haemoglobin of ox-blood contains - 336 per cent, of iron, 
and its molecular weight is 16,069 ; its capacity for carbon monoxide or 
oxygen, as calculated from its percentage of iron, is 1*34 c.c. for 1 grm., 
a figure practically identical with that obtained by direct experiment. 2 
This is probably also the case with haemoglobin obtained from the 
horse, dog, pig, rabbit, and fowl, for Bunge and others 3 have shown 
that the general percentage of iron is 0*335 per cent. Further, the 
amount of haemoglobin in human blood is about 14 per cent., and since 
1 grm. of haemoglobin can absorb about 1 "34 c.c, of oxygen, it follows that 
the amount of oxygen combined in arterial blood should be about 20 
volumes per cent., and actual experiment shows that this is the case. 4 
It is probable that some of Bohr's results are due to mixtures of 
pure and partly decomposed haemoglobin, and that some of the haemo- 
globin may be in the form of methaemoglobin. The same criticism 
may possibly apply to the results obtained by Halclane and Lorrain 
Smith. 5 
The oxygen in the blood of invertebrates. — In many of the invertebrate 
animals, haemoglobin, haemocyanin, and other proteids, which can enter into 
loose combination with oxygen, are found and play a part in the process of 
respiration. It is impossible, however, in a few Avords, to do justice to this 
interesting portion of comparative physiology ; for further details, the article 
by Halliburton 6 on the blood of invertebrate animals should be consulted. 
1 Arch. f. Physiol., Leipzig, 1894, S. 130. 
2 See also Hoppe-Seyler, Virchows ArcJiiv, Bd. xxix. S. f>98 ; Med.-chcm. Untcrsvch., 
1867, Bd. ii. S. 191 ; Preyer, " De hajmosdobino observationes et experimenta," Bonnse, 
1866, p. 19 ; Centralbl.f. d. vied. Wisscnsch., Berlin, 1866, No. 21. 
3 Jaqnet, Ztschr. f. jthysiol. Ohem., Strassburg, 1889, Bd. xiv. S. 289. 
4 See p. 761. 
5 Journ. Physiol., Cambridge and London, 1894, vol. xvi. p. 468. 
6 "Text-Book of Chemical Physiology and Pathology," London, 1891, pp. 316-330. Here 
numerous references to previous work on the subject will be found. Among subsequent 
papers may be mentioned those of Griffiths, Compt. rend. Acad. d. sc, Paris, 1892, 
tome cxv. pp. 259, 419, 474, 669, 738 ; cxvi. p. 1206. 
