7 7 2 CHEMISTR Y OF RESPIRA TION. 
was avoided in the analyse? made by Zuntz, by the addition of distilled water 
in sufficient quantity to maintain the concentration of the fluid at its original 
point. Preyer 1 found that the proportion of carbon dioxide in loose and in 
firm combination was as 2 to 3 -5. 
The next question to discuss is the nature of the substances with 
which the carbon dioxide is combined. The facts already mentioned 
show that these substances are to be sought chiefly in the serum. In 
the first place, analyses of the ash of serum show that the most important 
constituents are the alkalies ; thus, according to Bunge's 2 experiments, 
the ash from 1000 grms. of dog's serum contains 4-341 grms. sodium, of 
which 3*403 grms. is sufficient to saturate the chlorine. The remainder, 
0-878 grms. sodium, can combine with 0-623 grms. carbon dioxide (316 
c.c. at 0° and 760 mm.) to form sodium carbonate, and, in addition, with 
another equal quantity to form sodium bicarbonate. Thus calculated, 
a litre of plasma could hold 632 c.c. of carbon dioxide, or 63 volumes 
per cent, in chemical combination. This must be considered only as an 
approximate result, for the amount of sodium carbonate in serum cannot 
be accurately determined by an analysis of the ash or by titration, for 
the alkali is combined with other substances, especially with proteids. 3 
The alkalies of the blood are the most important constituents for 
holding carbon dioxide in combination. Serum freed from gas can 
combine with as much carbon dioxide as is necessary to form bicarbonates 
with its alkalies ; any reduction in the alkalinity of the blood is accom- 
panied by a decrease in carbon dioxide. Thus Walter 4 found only 
2 to 3 volumes per cent, of carbon dioxide in the blood of rabbits poisoned 
by hydrochloric acid : Geppert and Zuntz 5 observed that the alkalinity 
of the blood of rabbits was diminished by -the acid formed during tetanic 
muscular activity, and at the same time there was a decrease in the 
carbon dioxide of the blood. During diabetic coma the alkali of the blood 
appears to lie in great part neutralised by combination with /3-oxybutyric 
acid; 6 and Minkowski 7 found only 3'3 volumes per cent, of carbon 
dioxide in the blood of a patient suffering from diabetic coma. 
Another substance with which the carbon dioxide is supposed to 
combine in serum is disodium hydrogen phosphate 8 (Na.,HP0 4 ), with the 
formation of sodium bicarbonate and sodium Diphosphate. Thus — 
Na 2 HP0 4 + C0 2 + HX> = XaHC0 3 + NaH 2 P0 4 . 
Sertoli 9 and Mroczkowski, 10 however, found that the quantity of 
phosphoric acid in the serum is so small that, if allowance be made for 
that contained in lecithin and nuclein, the amount is quite insufficient 
1 Sitzungsb. d. k. Akad. d. Wissensch. Math.-nati<r"\ CI., Wien, Bd. xlix. S. 27. 
- Ztschr. f. Biol., Miinchen, 1876, Bd. xii. S. 204; "Lehrbueh der physiologischen 
und pathologischen Chemie," Leipzig, 1889, S. 254. 
3 Hoppe-Seyler, "Physiol. Chem.," Berlin, 1S79, Bd. iii. S. 502; Sertoli, Med.- 
chem. Untersuch,, Berlin, 1868, Heft 3, S. 350. 
4 Arch. f. exper. Path. u. Pharmakol., Leipzig, Bd. vii. 
5 Arch.f. d. ges. Physiol., Bonn, 1888, Bd. xlii. S. 189. See also this article, p. 714. 
6 Stadelmann, Arch. f. exper. Path. u. Pharmakol, Leipzig, Bd. vii. ; Minkowski, 
Hid., Bd. xviii. ; Mitth. a. d. med. Klin, zu Konigsbcrg, Leipzig. 1888. 
7 Loc. cit. 
8 Fernet, Ann. d. sc. nat., Paris, Se>. 4, tome viii. p. 160 ; Heidenhain and L. Meyer, 
Stud. d. physiol. Past, zu Breslau, Leipzig, 1863, Heft 2; Ann. d. Chem. u. Pfiarm., 
1862-63, Supp. Bd. ii. S. 157. 
9 Hoppe-Seyler, Med. -chem. Untersuch.. Berlin, 1868, Heft 3, S. 350. 
10 Centralbl. f. d. med. Wissensch., Berlin, 1878, No. 20, S. 356. 
