CONNECTION BETWEEN BLOOD AND ITS GASES. 765 



by three, in order that allowance may be made for the increased rate of 

 flow in the blood of an active limb. 



As regards the velocity of the circulation, Finkler 1 finds that the 

 difference between the arterial and venous blood increases as the velocity 

 diminishes. This relationship is well shown by Bernard's 2 observations 

 upon the submaxillary gland. When the gland is at rest the venous blood 

 is dark, but becomes almost arterial in colour when the gland becomes 

 active and its blood vessels are dilated by stimulation of the chorda 

 tympani. The difference between the arterial and venous blood is less 

 marked, but the total absorption of oxygen and production of carbon 

 dioxide are increased. 



In the last stage of asphyxia, the arterial blood contains only traces 

 of oxygen. Thus Ludwig 3 gives, as the result of six analyses made by 

 Setschenow and Holmgren upon asphyxiated dogs, 0*4 volume per cent, 

 oxygen, 3 per cent, nitrogen, and 54 per cent, carbon dioxide ; and Zuntz 4 

 has collected the results of nineteen analyses made by different observers, 5 

 and obtains an average of 0'96 volume per cent, oxygen, 2'07 per cent, 

 nitrogen, 49'53 per cent, carbon dioxide. These values Zuntz contrasts 

 with those obtained from averages of seventy-one analyses made by 

 Pfliiger and others upon normal arterial blood, namely, 18 '3 volumes per 

 cent, oxygen, 1*9 per cent, nitrogen, and 38'1 carbon dioxide; and he 

 shows that the ratio between the increase of carbon dioxide and the loss 

 of oxygen is O66 in asphyxia, as compared with 079 in the normal con- 

 dition. This difference is to be explained by the retention of some carbon 

 dioxide in the tissues, owing to the high tension of that gas in the blood. 



During apnoea the arterial blood is almost saturated with oxygen, and 

 contains about one-half its normal amount of carbon dioxide ; the venous 

 blood, on the other hand, contains less oxygen as well as less carbon 

 dioxide than it does in the normal condition. 6 These results confirm the 

 work of Pfliiger, 7 who found that during apnoea the respiratory exchange 

 was not greater or smaller than in the ordinary condition of respiration. 



The changes which the blood undergoes in passing through the brain 

 are much less marked than those which occur during its passage through 

 muscles. Even during marked activity the brain has a comparatively 

 small respiratory exchange. 8 



The nature of the connection between the blood and its gases. 

 Oxygen. Magnus 9 in 1836 concluded that the gases of the blood were 

 simply dissolved in that fluid, notwithstanding the fact that his experi- 

 ments showed that the quantity of oxygen in the blood was much greater 

 than the amount which could be dissolved in an equal volume of water 

 exposed to air. Justus Liebig, 10 however, pointed out that Eegnault and 

 Eeiset's n experiments showed that animals absorbed the same amount of 

 oxygen whether they breathed pure oxygen or air ; he therefore urged 



1 Arch.f. d. ges. Physiol., Bonn, 1875, Bd. x. S. 368. 



2 "Lemons sur les liquides de 1'organisme, " Paris, 1859, tome ii. p. 435 ; "Le9ons sur la 

 chaleur animale," Paris, 1876, p. 185. 



3 Wien. med. Jahrb., 1865, Bd. xxi. S. 145. 



4 Hermann's "Handbuch," Bd. iv. Th. 2, S. 43. 5 See Zuntz, loc. cit. 



6 Ewald, Arch. f. d. ges. Physiol., Bonn, 1873, Bd. vii. S. 575. 



7 Ibid., 1868, Bd. i. S. 100. 



8 Hill and Nabarro, Journ. Physiol. , Cambridge and London, 1895, vol. xviii. p. 218. 

 See also " Animal Heat," this Text-book, vol. i. p. 808. 



9 Ann. d. Phys. u. Chem., Leipzig, 1837, Bd. xl. S. 583 ; 1845, Bd. Ixvi. S. 177. 



10 Ann. d. Chem. u. Pharm., 1851, Bd. Ixxix. S. 112. 



11 Ann. de chim. etphys., Paris, 1849, Se'r. 3, tome xxvi. 



