BLOOD GASES. 21 



Haemoglobin contains -g-J- of its weight of iron. Solution of hemoglobin 

 exhibits before the spectroscope characteristic absorption bands. Very dilute 

 solution shows one band to the blue side of the D line ; if the solution is 

 stronger, a second band appears to the red side of the E line ; by still more 

 concentrated liquids, the blue and violet rays are entirely absorbed, while 

 the two bands become confluent. 



When blood is allowed to stand at ordinary temperatures, its haemoglobin 

 is soon decomposed, yielding haematin, a proteid body, and other products. 

 The same thing happens much more rapidly when solution of hasmoglobiu is 

 acted on by alkalies, in which case haematin and alkali-albuminates are 

 formed. In presence of weak acids, haemoglobin yields haematoin (so-called 

 "acid haematin ") and acid albuminate. 



Hcematin (C aa H 34 N 4 Fe O 5 ) is obtained when weak potash solution acts 

 on blood or solution of haemoglobin ivith access of air. On neutralizing, solid 

 haematin is precipitated. It is insoluble in water, alcohol, and ether, and 

 uncrystallizable. 



The absorption spectrum of haematin presents a broad band to the red side 

 of the D line. After reduction by alkaline sulphides it shows two charac- 

 teristic bands, one in the yellow, the other in the green part of the spectrum. 

 When dried blood is warmed with glacial acetic acid, it yields crystals of 

 hcemin (haematin + HC1). 



Solution of haemoglobin associates nitric oxide and carbonic oxide in the 

 same volume as oxygen. When oxygenated solution of haemoglobin or of 

 blood is acted on by carbonic oxide, its associated oxygen is replaced by that 

 gas. The solution acquires a colour which closely resembles that of arterial 

 blood, but is not affected by reducing agents. 



The quantity of oxygen yielded to the barometer vacuum 

 by any quantity of aerated defibrinated blood is equal to 

 the quantity associated by the haemoglobin contained in 

 the blood,////^ the quantity absorbed by the plasma ; (hence 

 for every 5 centigrammes of iron i8'7 cubic centimeters 

 of oxygen at o and 760 m.m.) In ordinary arterial blood 

 the yield of oxygen is a little less. Arterial blood at 

 40 yields about 40 per cent, of its volume of CO 2 , as 

 measured at o and 760 m.m. The alkaline carbonates are 

 decomposed in the vacuum without the addition of an acid. 



The human body contains about $ of its weight of 

 blood. 



In the examination of blood for clinical purposes, it is 

 chiefly important to determine the percentage of haemo- 

 globin and the alkaline reaction. 



