CA USES OF THE EXCHANGE OF GASES. 773 



to play any important part in combining with carbon dioxide. Bunge, 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 loose 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 carbon 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 18 '4, 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 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. 



CARBON DIOXIDE, Tissues ^ Blood ^ Alveolar air. 



1 Ztschr. f. Biol., Miiiichen, 1876, Bd. xii. S. 206; " Lehrbuch der physiologischen und 

 pathologischen Chemie," Leipzig, 1889, S. 256. 



2 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. CL, Leipzig, 

 1867, Bd. xix. S. 30; Zuntz, Centralbl. f. 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 Beitr. z. Physiol. Carl Ludwig z. s. 70 Geburtst., Leipzig, 1887, S. 164; Jahresb. 

 ii. d. Fortschr. d. Thier-Chem., Wiesbaden, Bd. xvii. S. 115. 



7 Jahresb. u. d. Fortschr. d. Thier-Chem., Wiesbaden, Bd. xvii. S. 115. 



