GENERAL PROPERTIES: THE CORPUSCLES. 427 



section on Respiration. Hemoglobin forms with carbon monoxid 

 gas (CO) a compound, similar to oxyhemoglobin, which is known 

 as carbon monoxid hemoglobin. In this compomid also the union 

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

 molecule of the gas. The compound formed differs, however, 

 from oxyhemoglobin in being much more stable, and it is for this 

 reason that the breathing of carbon monoxid gas is liable to prove 

 fatal. The CO unites with the hemoglobin, forming a firm com- 

 pound: the tissues of the body are thereby prevented from obtain- 

 ing their necessary oxygen, and death results from suffocation or 

 asphyxia. Carbon monoxid forms one of the constituents of 

 coal-gas. The well-known fatal effect of breathing coal-gas for 

 some time, as in the case of individuals sleeping in a room in which 

 gas is escaping, is traceable directly to the carbon monoxid. Nitric 

 oxid (NO) forms also with hemoglobin a definite compound that 

 is even more stable than the CO hemoglobin; if, therefore, this 

 gas were brought into contact with the blood, it would cause death 

 in the same way as the CO. 



Oxyhemoglobin, carbon monoxid hemoglobin, and nitric oxid 

 hemoglobin are similar compounds. Each is formed, apparently, 

 by a definite combination of the gas with the hematin portion of the 

 hemoglobin molecule, and a given weight of hemoglobin unites 

 presumably with an equal volume of each gas. In marked contrast 

 to these facts, Bohr* has shown that hemoglobin forms a compound 

 with carbon dioxid gas, carbohemoglobin, in which the quantitative 

 relationship of the gas to the hemoglobin differs from that shown 

 by oxygen. It is not probable that this property of combining 

 with CO2 is of importance in explaining the transportation of CO2 

 in the blood. Under the conditions of reaction and carbon dioxid 

 pressure found in the blood very little CO2 can be combined in 

 this way. We shall find later that hemoglobin plays a large part 

 as a carrier of CO2, but it owes this property to the alkalies it 

 contains rather than to the formation of the compound carbo- 

 hemoglobin. 



Presence of Iron in the Molecule. — It is probable that iron 

 is quite generally present in the animal tissues in connection with 

 nuclein compounds, but its existence in hemoglobin is noteworthy 

 because it has long been known, and because the important property 

 of combining with oxygen seems to be connected with the presence 

 of this element. According to recent analyses, the proportion of 

 iron in hemoglobin is constant, lying between 0.33 and 0.34 per 

 cent.J The amount of hemoglobin in blood may be determined, 



* Skandinavisches Archiv. f. Physiologie," 3, 47, 1892, and 16, 402. 1904. 

 t Butterfield, "Zeit. f. physiol. Chemie," 62, 173, 1909. 



