436 



THE BLOOD. 



[CH. XXVI 



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 b obtained in crystals isomorphou 

 with oxy- and CO-hsemoglobin. It also has a similar spectrum. 



Fig. 368. Hsemoglobinometer of Dr. Gowers 



It is even more stable than CO-hsemoglobin ; it has no practical 

 interest, but is of theoretical importance as completing the series. 



Bohr has advanced a theory that haemoglobin forms a compound with 

 carbonic acid, and that there are numerous oxyhaamoglobins containing 

 different amounts of oxygen, but his views have not been accepted. 



Estimation of Haemoglobin. The most exact method is by the estima- 

 tion 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 colorimetric methods have been proposed which, though not 

 so exact, have the advantage of simplicity. 



G-owers's Hwmogrlobinometer. The apparatus (fig. 368) consists of two 

 glass tubes of the same size. One contains glycerine 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 oxyhsmoglobin in the blood is normal. If 

 it has to be diluted more largely, the oxyhasmoglobin is in excess ; if to a 

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



