78 



ANIMAL CHEMISTRY. 



This carbonic acid is not separated from 

 the serum; for the serum does not possess 

 the property, when in contact with oxygen, 

 of giving off carbonic acid. On the con- 

 trary, when separated from the globules, it 

 absorbs fro-ii naif its volume to an equal 

 volume of carbonic acid, and, at ordinary 

 temperatures, is not saturated with that gas. 

 (See the article " Blut," in the " Handwor- 

 terbuch der Chemie, von Poggendorff, Wuh- 

 ler, und Liebig, p. 877.) 



Arterial blood, when drawn from the 

 body, is soon altered ; its florid colour be- 

 comes dark red. The florid blood, which 

 owes its colour to the globules, becomes 

 dark by the action of carbonic acid, and this 

 change of colour affects the globules, for 

 florid blood absorbs a number of gases which 

 do not dissolve in the fluid part of the blood 

 when separated from the globules. It is 

 evident, therefore, tliat the globules liave the 

 power of combining with gases. 



The globules of the blood change their 

 colour in different gases; and this change 

 may be owing either to a combination or to 

 a decomposition. 



Sulphuretted hvdrogen turns them black- 

 ish green and finally black ; and the original 

 red colour cannot, in this case, be restored 

 by contact with oxygen. Here a decompo- 

 sition has obviously taken place. 



The globules darkened by carbonic acid 

 become again florid in oxygen, with disen- 

 gagement of carbonic acid. The same thing 

 takes place in nitrous oxide. It is clear that 

 they have here undergone no decomposition, 

 and, consequently, they possess the power 

 of combining with gases, while the compound 

 they form with carbonic acid is destroyed by 

 oxygen. When left to themselves, out 01 

 the body, the compound formed with oxy- 

 gen again becomes dark, but does not 

 recover its florid colour a second time by 

 the action of oxygen. 



The globules of the blood contain a com- 

 pound of iron. From the never-failing 

 presence of iron in red blood, we must con- 

 clude, that it is unquestionably necessary 

 to animal life; and, since physiology has 

 proved, that the globules take no share in 

 the process of nutrition, it cannot be doubted 

 that they play a part in the process of re- 

 spiration. 



The compound of iron in the globules 

 has the characters of an oxidized com- 

 pound ; for it is decomposed by sulphuretted 

 hydrogen, exactly in the same way as the 

 oxides or other analogous compounds of 

 iron. By means of diluted mineral acids, 

 peroxide 'sesquioxide) of iron may be ex- 

 tracted, at the ordinary temperature, from 

 the fresh or dried red colouring matter of 

 the blood. 



The characters of the compounds of iron 

 may, perhaps, assist us to explain the share 

 which that metal takes in the respiratory 

 process. No other metal can be compared 

 with iron, for the remarkable properties of 

 its compounds. 



The compounds of protoxide of iron pos- 

 sess the property of depriving other oxidized 

 compounds of oxygen; while the compounds 

 of peroxide of iron, under other circum- 

 stances, give up oxygen with the utmost 

 facility. 



Hydra ted peroxide of iron, in contact 

 with organic matters destitute of sulphur, 

 is converted into carbonate of the protoxide. 



Carbonate of protoxide of iron, in con- 

 tact with water and oxygen, is decomposed ; 

 all the carbonic acid is given off, and, by 

 absorption of oxygen, it passes into the 

 hydrated peroxide, which may again be con- 

 verted into a compound of the protoxide. 



Not only the oxides of iron, but also the 

 cyanides of that metal, exhibit similar pro* 

 perties. Prussian blue contains iron ip 

 combination with all the organic elements 

 of the body ; hydrogen and oxygen (water) 

 carbon and nitrogen (cyanogen.) 



When it is exposed to light, cyanogen is 

 given off, and it becomes white ; in the dark 

 it extracts oxygen, and recovers its blue 

 colour. 



All these observations, taken together, 

 lead to the opinion that the globules of arte- 

 rial blood contain a compound of iron satu- 

 rated with oxygen, which, in the living 

 blood, loses its oxygen during its passage 

 through the capillaries. The same thing 

 occurs when it is separated from the body, 

 and begins to undergo decomposition (to pu- 

 trefy.) The compound, rich in oxygen, 

 passes, therefore, by the loss of oxygen ("re- 

 duction) into one far less charged with tha: 

 element. One of the products of oxidation 

 formed in this process is carbonic acid. The 

 compound of iron in the venous blood pos- 

 sesses the property of combining with car- 

 bonic acid ; and it is obvious, that the glo- 

 bules of the arterial blood, after losing a part 

 of their oxygen, will, if they meet with car- 

 bonic acid, combine with that substance. 



When they reach the lungs, they wil' 

 again take up the oxygen they have lost ; 

 for every volume of oxygen absorbed, a cor- 

 responding volume of carbonic acid will be 

 separated ; they will return to their former 

 state ; that is, they will again acquire the 

 power of giving off oxygen. 



For every volume of oxygen which the 

 globules can give off, there will be formed 

 (as carbonic acid contains its own volume 

 of oxygen, without condensation) neither 

 more nor less than an equal volume of car- 

 bonic acid. For every volume of oxygen 

 which the globules are capable of absorbing, 

 no more carbonic acid can possibly be sepa- 

 rated than the volume of oxygen can pro- 

 duce. 



When carbonate of protoxide of iron, by 

 the absorption of oxygen, passes into the 

 hydrated peroxide, there are given off, for 

 every volume of oxygen necessary to the 

 change from protoxide to peroxide, four vo- 

 lumes of carbonic acid gas. 



But from one volume of oxygen only on? 

 volume of cabronic acid can be produced, 



