470 THE BLOOD [CH. XXIX. 



globin is discharged, and this may be collected and measured as in the method 

 described on p. 364. This discharge of oxygen from oxy haemoglobin is at first 

 sight puzzling, because, as just stated, methaemoglobin contains the same amount 

 of oxygen that is present in oxyhaemoglobin. What occurs is that after the oxygen 

 is discharged from oxyhaemoglobin, an equal quantity of oxygen, due to the 

 oxidising action of the reagents added, takes its place ; this new oxygen, how- 

 ever, is combined in some way different from that which was previously united 

 to the haemoglobin. (Haldane.) 



Carbonic oxide haemoglobin may be readily prepared by passing 

 a stream of carbonic oxide or coal gas through blood or through a 

 solution of oxyhaemoglobin. It has a peculiar cherry-red colour. Its 

 absorption spectrum is very like that of oxyhaemoglobin, but the two 

 bands are slightly nearer the violet end of the spectrum (spectrum 4 

 in coloured plate). Seducing agents, such as ammonium sulphide, do 

 not change it ; the gas is more firmly combined than the oxygen in 

 haemoglobin. CO -haemoglobin forms crystals like those of oxyhaemo- 

 globin. It resists putrefaction for a very long time. 



Carbonic oxide is given off during the imperfect combustion of 

 carbon such as occurs in charcoal stoves or during the explosions that 

 occur in coal-mines ; it acts as a powerful poison, by combining with 

 the haemoglobin of the blood, and thus interferes with normal respira- 

 tory processes. The bright colour of the blood in both arteries and 

 veins, and its resistance to reducing-agents, are in such cases 

 characteristic. 



Nitric Oxide Haemoglobin. When ammonia is added to blood, 

 and then a stream of nitric oxide passed through it, this compound 

 is formed. It may be obtained in crystals isomorphous with oxy- 

 and CO-haemogloljin. It also has a similar spectrum. It is even 

 more stable than CO-haemoglobin ; it has no practical interest, but is 

 of theoretical importance as completing the series. 



Estimation of Haemoglobin. The most exact method is by the estimation of 

 the amount of iron (dry haemoglobin containing "42 per cent, of iron) in the ash of a 

 given specimen of blood, but as this is a somewhat complicated process, various 

 coloriraetric methods have been proposed which, though not so exact, have the 

 advantage of simplicity. 



Gowers' Hsemoglobinometer. The apparatus (fig. 336) consists of two glass 

 tubes of the same size. One contains glycerin jelly tinted with carmine to a 

 standard colour viz., that of normal blood diluted 100 times with distilled water. 

 The finger is pricked and 20 cubic millimetres of blood are measured out by the 

 capillary pipette B. This is blown out into the other tube and diluted with distilled 

 water, added drop by drop from the pipette stopper of the bottle A, until the tint 

 of the diluted blood reaches the standard colour. This tube is graduated into 100 

 parts. If the tint of the diluted blood is the same as the standard when the tube is 

 filled up to the graduation 100, the quantity of oxyhaemoglobin in the blood is 

 normal. If it has to be diluted more largely, the oxyhaemoglobin is in excess ; if to 

 a smaller extent, it is less than normal. If the blood has, for instance, to be diluted 

 up to the graduation 50, the amount of haemoglobin is only half what it ought to 

 be 50 per cent, of the normal and so for other percentages. 



Haldane's Modification of Gowers' Instrument is the one most frequently 

 used now, and gives very accurate results. Instead of tinted gelatin, the standard 

 of comparison is a sealed tube filled with a solution of carbonic oxide haemoglobin. 



