BLOOD. 39 



thereby prevented from obtaining their necessary oxygen, and death results 

 from suffocation or asphyxia. Carbon monoxide forms one of the constituents 

 of coal-gas. The well-known fatal effect of breathing coal-gas for some time, 

 as in the case of individuals sleeping in a room where gas is escaping, is trace- 

 able directly to the carbon monoxide. Nitric oxide (NO) forms also with 

 haemoglobin a definite compound that is even more stable than the CO- 

 haemoglobin ; if, therefore, this gas were brought into contact with the blood, 

 it would cause death in the same way as the CO. 



Oxyhemoglobin, carbon-monoxide haemoglobin, and nitric-oxide haemoglo- 

 bin are similar compounds. Each is formed, apparently, by a definite combina- 

 tion of the gas with the haemochromogen portion of the haemoglobin molecule. 

 and a given weight of haemoglobin unites presumably with an equal volume of 

 each gas. In marked contrast tothese facts, Bohr x has shown that haemoglobin 

 forms a compound with carbon-dioxide gas, carbo-hcemoglobin, in which the 

 quantitative relationship of the gas to the haemoglobin differs from that shown 

 by oxygen. In a mixture of O and C0 2 each gas is absorbed by haemoglobin 

 solutions independently of the other, so that a solution of haemoglobin nearly 

 saturated with oxygen can unite with as much C0 2 as though it held no oxygen 

 in combination. Bohr suggests, therefore, that the O and the CO L> must unite 

 with different portions of the haemoglobin — the oxygen with the pigment portion, 

 the haemochromogen, and the C0 2 possibly with the proteid portion. It seems 

 probable that haemoglobin plays a part in the transportion of the earl ion 

 dioxide as well as the oxygen of the blood, but its exact value in this respect 

 as compared with the blood-plasma, which also acts as a carrier of CO a , has 

 not been definitely determined (see Respiration). 



Presence of Iron in the Molecule. — It is probable that iron is quite 

 generally present in the animal tissues in connection with nuclein compounds, 

 but its existence in haemoglobin is noteworthy because it has long been known 

 and because the important property of combining with oxygen seems to be 

 connected with the presence of this element. According to the analyses 

 made, the proportion of iron in haemoglobin varies somewhat in different 

 animals: the figures given arc from 0.335 to 0.47 per cent. The amount of 

 haemoglobin in blood may he determined, therefore, by making a quantitative 

 determination of the iron. The amount of oxygen with which haemoglobin 

 will combine may he expressed by saying that one molecule of oxygen will 

 be fixed for each atom of iron in the haemoglobin molecule. In the decom- 

 position of haemoglobin into globulin and haematin, which has been spoken of 

 above, the iron is retained in the haematin. 



Crystals. — Haemoglobin maybe obtained readily in the form of crystals 

 (Fig. 1). As usually prepared, these crystals are really oxyhaemoglobin, but 

 it has been shown that reduced haemoglobin also crystallizes, although with 

 more difficulty. Haemoglobin from the blood of different animals varies to a 

 marked degree in resped to the power of crystallization. From the blood of 

 the rat, do^, cat, guinea-pig, and horse, crystals arc readily obtained, while 

 haemoglobin from the blood of man and of most of the vertebrates crystallizes 



1 Skandivavisches Archivf&r Physiologie, 1892, Bd. '■'<. S. -17. 



