

METH.EMOGLOBIN. 23 



but two well-marked absorption-bands exist between D and E. The line nearest 



D, i.e., next the red end of the spectrum, sometimes designated by the letter (a) 

 is narrow, sharply denned, and black at its centre, and its position corresponds to 

 the wave-length 579. The other absorption-band near E, conveniently designated 

 by (ft), is broader, not so dark, and its edges are less sharply denned. Its centre 

 corresponds to the wave-length 553*8. In very dilute solutions the a band is the 

 only one visible. In a strong solution, as shown in fig. 1 7, the two bands fuse, but 

 are again made visible as two on dilution of the blood.] 



Reduction of Oxyhemoglobin. It gives up its O very readily, however, even 

 when means which set free absorbed gases are used. It is reduced by the removal 

 of the gases by the air-pump, by the conduction through its solution of other gases 

 (CO), and by heating to the boiling-point. In the circulating blood its O is very 

 rapidly given up to the tissues, so that in suffocated animals only reduced /uemo- 

 globin is found in the arteries. Some constituents of the serum and sugar remove 

 its O. By adding to a solution of oxyhemoglobin reducing substances e.g., 

 ammonium sulphide, iron filings, or Stokes's fluid [tartaric acid, iron proto-sulphate, 

 and excess of ammonia] the two absorption-bands of the spectrum disappear, and 

 reduced haemoglobin (gas-free), with one absorption-band, is formed. The colour 

 changes from a bright red to a purplish or claret tint. The two bands are 

 reproduced by shaking the reduced haemoglobin with air, whereby 2 Hb is again 

 formed. Solutions of oxyhemoglobin are readily distinguished by their scarlet 

 colour from the purplish tint of reduced haemoglobin. 



[The single absorption-band (fig. 17, 4) designated by the letter (y), lying about 

 midway between the position of the two previous bands, is broader, fainter, less 

 deeply shaded, and its centre is about, but not quite, intermediate between D and 



E. It extends between the wave-lengths 595 and 538, and is blackest opposite the 

 wave-length 550, so that it lies nearer D than E. At the same time more of the 

 blue rays are transmitted. On dilution the band is not resolved into two, but 

 simply becomes fainter and disappears.] 



[Haemoglobin has certain remarkable characters : (1) Although it is a crystalloid 

 body it diffuses with difficulty through an animal membrane, owing to the large 

 size of its molecule. (2) It readily combines with O to form an unstable and loose 

 chemical compound, oxyhaemoglobin. (3) This it gives up readily to the tissues 

 or other deoxidising reagents. (4) Its composition is very complex, for, in addition 

 to the ordinary elements present in proteids, it contains a remarkable amount of 

 iron (0*4 per cent.).] 



If a string be tied round the base of two fingers so as to interrupt the circulation, spectro- 

 scopic examination shows that the oxyhaemoglobin rapidly passes into reduced Hb ( Vierordt). 

 Cold delays this reduction ; it is accelerated in youth, during muscular activity, or by suppressed 

 respiration, and usually also during fever. 



The spectroscopic examination of small blood-stains is often of the utmost forensic import- 

 ance. A minimal drop is sufficient. Dissolve the stain in a few drops of distilled water, and 

 place the solution in a thin glass tube in front of the slit of the spectroscope. 



Para-hsemoglobin. If 2 Hb be preserved under alcohol it passes into a modified form, 

 which is insoluble in water (Nencki and Siebcr). 



2. Methaemoglobin is a more stable, crystalline compound (Hoppe-Seyler). It 

 contains the same amount of O as 2 Hb, but in a different chemical union, while 

 the O is also more firmly united with it. It shows four absorption-bands like 

 haematin in acid solution (fig. 17, 5), of which that between C and D is distinct ; 

 the second is very indistinct, while the third and fourth readily fuse, so that these 

 last two bands are only well seen with good apparatus. 



It is produced spontaneously in old brown blood-stains, in the crusts of bloody wounds, in blood 

 cysts, and in bloody urine. Chemically, it can be prepared from a solution of Hb, by the action of 

 potassic ferri-cyanide (Jdderholm) or potassic chlorate (Marchand), [or by adding to a solution 

 of Hb a freshly prepared solution of potassic permanganate], and in non-laky blood by alloxantin 



