CA USES OF THE EXCHANGE OF GASES. 773 
to play any important part in combining with carbon dioxide. Bimge, 1 on 
the other hand, maintains that in dog's blood the quantity of phosphoric 
acid is sufficient, and that only a small quantity is combined with alkalies 
in the plasma : he agrees, however, with the previous observers, that the 
amount of phosphoric acid in the blood of the ox and the pig is very small. 
There is also evidence to show that the proteids, especially the 
globulin of serum, play some part in forming combinations with carbon 
dioxide. Setschenow 2 considered that the globulin formed a combina- 
tion with the carbon dioxide, whereas Sertoli held that the globulin 
acted as an acid, and in the serum was combined with an alkali. 
The blood corpuscles contain about one-third of the total carbon 
dioxide found in the blood. 3 The gas is in louse chemical combination 
probably with the alkali of the phosphates, globulin, and haemoglobin 
of the corpuscles, and directly with the haemoglobin. Setschenow 
calculates that in 100 volumes of blood the red corpuscles contain 10 
volumes, and the white corpuscles 2 - 5 volumes of carbon dioxide. 
The experiments of Setschenow, 4 Zuntz, 5 Bohr, 6 and Torup 7 show 
that carl urn dioxide combines with haemoglobin even in the absence of an 
alkali. A solution of pure crystallised haemoglobin absorbs more carbon 
dioxide than does an equal volume of water, and the amount of gas 
absorbed is relatively large for low pressures, but relatively small for 
high pressures. According to Bohr, 1 grm. of haemoglobin at IS 1 "-!, and 
under a pressure of 30 mm., combines with 2'4 c.c. of carbon dioxide ; 
the pigmented portion of the haemoglobin is supposed to combine with 
oxygen and the proteid portion with carbon dioxide. 
Further investigation, however, is necessary before it will be possible 
with any exactitude to decide the relative importance of the different 
combinations with the carbon dioxide of the blood. 
The causes of the exchange of gases between the air in the 
lungs and the blood.— The oxygen of the blood is derived from the air 
in the alveoli of the lungs : the carbon dioxide in the expired air comes 
from the pulmonary blood, and ultimately from the tissues of the body. 
The inspired air contains at 0° and 760 mm. 20 - 96 volumes per cent. 
of oxygen, the expired air about 16 per cent., and the tissues no free 
oxygen ; the carbon dioxide is 0'03 volumes per cent, in the inspired 
air, about 4 in the expired air, and in the tissues is being constantly 
produced. There would, therefore, appear to be sufficient causes, both 
physical and chemical, to determine the passage of the oxygen inwards 
and of the carbon dioxide outwards. 
Oxygen, Alveolar air ^ Blood — ^> Tissues. 
Carbox Dioxide, Tissues y Blood ^ Alveolar air. 
1 Ztschr.f. Biol., Miinchen, 1876, Bd. xii. S. 206; " Lehrbuch der physiologischen und 
pathologisehen Chemie," Leipzig, 1889, S. 256. 
- Arch. f. d. ges. Physiol.. Bonn, 1874, Bd. viii. S. 1 ; Centralbl. f. d. med. Wissensch., 
Berlin. 1877, No. 35; 1879, No. 21 : Ber. d. deutsch. chem. Gesellsch., Berlin, 1879, Bd. xii. 
S. 855 ; Mem. Acad. imp. d. sc. de St. Petersbourg, 1879, tome xxvi. No. 13. 
3 Alex. Schmidt, Ber. d. k. sacks. Gesellsch. d. Wissensch. Math.-phys. CI., Leipzig, 
1867, Bd. xix. S. 30; Zuntz, Centralbl./. d. med. Wissensch., Berlin,' 1867, S. 529; Her- 
mann's "Handbuch," Bd. iv. Th. 2, S. 72 ; Fredericq, "Recherches sur la constitution du 
plasma sanguin," Gand, 1878, p. 49. 
4 Centralbl. f. d. med. Wissensch., Berlin, 1877. 
5 Hermann's "Handbuch," Bd. iv. Th. 2, S. 76. 
6 Beit r. z. Physiol. Carl Ludwig z. s. 70 Geburtst., Leipzig, 1887, S. 164; Jahresb. 
ii. d. Fortschr. d. Thier-Chem. , Wiesbaden, Bd. xvii. S. 115. 
1 Jahresb. ii. d. Fortschr. d. Thier-Chem., Wiesbaden, Bd. xvii. S. 115. 
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