336 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



is of enormous size. The molecular formula for haemochromogen is much 

 simpler; it is usually given as C 34 H 36 N 4 FeO 6 . The exact amount of haemoglobin 

 in human blood varies naturally with the individual and with different condi- 

 tions of life. According to Preyer, 1 the average amount for the adult male is 

 14 grams of haemoglobin to each 100 grams of blood. It is estimated that in 

 the blood of a man weighing 68 kilos, there are contained about 750 grams of 

 haemoglobin, which is distributed among some twenty-five trillions of corpuscles, 

 giving a total superficial area of about 3200 square meters. Practically all of 

 this large surface of haemoglobin is available for the absorption of oxygen 

 from the air in the lungs, for, owing to the great number and the minute 

 size of the capillaries, the blood, in passing through a capillary area, becomes 

 subdivided to such an extent that the red corpuscles stream through the capil- 

 laries, one may say, in single file. In circulating through the lungs, therefore, 

 each corpuscle becomes exposed more or less completely to the action of the 

 air, and the utilization of the entire quantity of haemoglobin must be nearly 

 perfect. It may be worth while to call attention to the fact that the biconcave 

 form of the red corpuscle increases the superficies of the corpuscle and tends 

 to make the surface exposure of the haemoglobin more complete. 



Compounds with Oxygen and other Gases. Haemoglobin has the 

 property of uniting with oxygen gas in certain definite proportions, forming a 

 true chemical compound. This compound is known as oxyhcemoglobin ; 

 it is formed whenever blood or haemoglobin solutions are exposed to air or 

 otherwise brought into contact with oxygen. Each molecule of haemoglobin 

 is supposed to combine with one molecule of oxygen, and it is usually estimated 

 that 1 gram of dried haemoglobin (dog) can take up 1.59 c.c. of oxygen 

 measured at C. and 760 mm. of barometric pressure. Oxy hemoglobin is 

 not a very firm compound. If placed in an atmosphere containing no oxy- 

 gen, it will be dissociated, giving off free oxygen and leaving behind haemo- 

 globin, or, as it is often called by way of distinction, " reduced haemoglobin." 

 This power of combining with oxygen to form a loose chemical compound, 

 which in turn can be dissociated easily when the oxygen-pressure is lowered, 

 makes possible the function of haemoglobin in the blood as the carrier of 

 oxygen from the lungs to the tissues. The details of this process will be 

 described in the section on Respiration. Haemoglobin forms with carbon- 

 monoxide gas (CO) a compound, similar to oxyhaemoglobin, which is 

 known as carbon-monoxide haemoglobin. In this compound also the union 

 takes place in the proportion of one molecule of haemoglobin to one 

 molecule of the gas. The compound formed differs, however, from oxy- 

 haemoglobin in being much more stable, and it is for this reason that the 

 breathing of carbon monoxide gas is liable to prove fatal. The CO unites 

 with the haemoglobin, forming a firm compound ; the tissues of the body are 

 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, 



1 Die Blutkrystalle, Jena, 1871. 



