358 RESPIRATION. 



the action of the mercurial pump, they will give off a definite quantity of 

 carbonic oxide, 1 gramme of the crystals yielding 1.59 c.c. of the gas. In 

 fact haemoglobin combines loosely with carbonic oxide just as it does with 

 oxygen ; but its affinity with the former is greater than with the latter. 

 While carbonic oxide readily turns out oxygen, oxygen cannot so readily 

 turn out carbonic oxide. Indeed, carbonic oxide has been used as a means 

 of driving out and measuring the quantity of oxygen present in any given 

 blood. This property of carbonic oxide explains its poisonous nature. 

 When the gas is breathed, the reduced and the unreduced hsemoglobin of 

 the venous blood unite with the carbonic oxide, and hence the peculiar, 

 bright cherry-red color observable in the blood and tissues in cases of poison- 

 ing by this gas. The carbonic-oxide hsemoglobin, however, is of no use in 

 respiration ; it is not an oxygen-carrier, nay more, it will not readily, though 

 it does so slowly and eventually, give up its carbonic oxide for oxygen, when 

 the poisonous gas ceases to enter the chest and is replaced by pure air. The 

 organism is killed by suffocation, by want of oxygen, in spite of the blood 

 not assuming any dark venous color ; to adopt a phrase which has been 

 used, the corpuscles are paralyzed. 



Hsemoglobin smilarly forms a compound, having a characteristic spec- 

 trum, with nitric oxide, more stable even than that with carbonic oxide. 



It has been supposed by some that the oxygen thus associated with hsemo- 

 globin is in the condition known as ozone ; but the arguments urged in sup- 

 port of this view are inconclusive. 



Products of the Decomposition of Hemoglobin. 



293. Although a crystalline body, hsemoglobin diffuses with great diffi- 

 culty. This arises from the fact that it is in part a proteid body ; it consists 

 of a colorless proteid, associated with a colored substance, which may be 

 separated out from the hsemoglobin, though not in the exact condition in 

 which it naturally exists in the compound ; this substance when separated 

 out appears as a brownish-red body known as hcematin. All the iron be- 

 longing to the hsemoglobin is in reality attached to the hsematin. A solution 

 of hsemoglobin, when heated, coagulates, the exact degree at which the 

 coagulation takes place depending on the amount of dilution ; at the same 

 time it turns brown from the setting free of the hsematin. If a strong solu- 

 tion of hsemoglobin be treated with acetic (or other) acid, the same brown 

 color, from the appearance of hsematin, is observed. The proteid constitu- 

 ent, however, is not coagulated, but by the action of the acid passes into 

 the state of acid-albumin. On adding ether to the mixture, and shaking, 

 the hsematin is dissolved in the supernatant acid ether, which it co'lors a 

 dark red, and which, examined with the spectroscope, is found to possess a 

 well-marked spectrum, the spectrum of the so-called acid hsematin of Stokes 

 (Fig. 98, 6). The proteid in the water below the ether appears in a coagu- 

 lated form owing to the action of the ether. In a somewhat similar manner 

 alkalies split up hsemoglobin into a proteid constituent and hsematin. 



The exact nature of the proteid constituent of hsemoglobin has not as 

 yet been clearly determined. It was supposed to be globulin (hence the 

 name hsematoglobulin, contracted into hsemoglobin), but though belonging 

 to the globulin family, has characters of its own ; it is possibly a mixture of 

 two or more distinct proteids. It has been provisionally named globin and 

 is said to be free from ash. 



294. Hsematin when separated from its proteid fellow, and purified, 

 appears as a dark-brown amorphous powder, or as a scaly mass with a 



