832 SPECIAL PHYSIOLOGY. 



systemic capillaries, it is partially deoxygenated, to supply the wants 

 of the disintegrating tissues, by a so-called parenchymatous respiration ; 

 on returning to the lungs, it is once more reoxygenated. 



The various alterations in the color of the blood, noticed in different 

 conditions, accord with this conclusion. Thus the blood is unusually 

 dark as it returns from the muscles, and the depth of its color is in 

 exact proportion to the activity of those muscles, when, as we shall 

 see, it also contains the most carbonic acid. On the other hand, the 

 venous blood returning from glands in a state of active secretion, is of 

 a bright scarlet hue; whereas, when the glands are inactive, it is dark 

 (pp. 264, 522, 756.) In the latter case, the quantity of blood passing 

 through the gland is small; nutrition proper is going on, and a pro- 

 portional quantity of carbonic acid is formed and taken up ; whereas 

 for active secretion, the conditions existing are, a large supply of 

 blood, with a proportionally less amount of deoxygenation. Again, it 

 has been noticed that, at high temperatures, there is much less differ- 

 ence in the color of the arterial and venous blood-current, and also a 

 less amount of respiratory interchange; whereas, at low temperatures, 

 the difference of color is greater, and so likewise is the activity of the 

 respiratory process. In anaemia, in the state of hibernation, and also 

 in sleep, the venous blood has the same color as the arterial; and both 

 the pulmonary and the parenchymatous respiration are imperfectly per- 

 formed. Lastly, in asphyxia and in cholera the blood is exceedingly 

 dark, and, in both diseases, contains unusually large quantities of car- 

 bonic acid. 



A further result of these researches, is to show that the oxygen 

 carried through the body by the blood is, to a large extent, actually 

 chemically combined with it, i. e., with the cruorin of the red corpus- 

 cles, though some must be merely dissolved in the liquor sanguinis, 

 and all must pass through that fluid, to enter and escape from the 

 corpuscles. But that a certain portion of the oxygen is retained in 

 the liquor sanguinis, is shown by the fact, that the clot of dark venous 

 blood assumes a bright hue when placed in the serum of arterial blood, 

 or even of the scarlet venous blood returning from an actively secre- 

 ting gland. It is uncertain whether any of the carbonic acid is spe- 

 cially attached to the red corpuscles ; it would rather seem not. The 

 coagulum of the scarlet venous blood from a gland, as well as that of 

 arterial blood, becomes darkened, when placed in the serum of dark 

 venous blood; so that carbonic acid certainly exists in the liquor 

 sanguinis of venous blood. It appears to be partly dissolved in the 

 serum, and is partly, perhaps, in a state of loose chemical combination. 



Changes in the Fibrin of the Blood. 



During the aeration of the blood in the lungs, and perhaps as a 

 special result of the action of oxygen absorbed from the air, the 

 amount of fibrin is increased in arterial, as compared with that in 

 yenous blood; a difference also exists in the coagulating power of the 

 arterial fibrin, which forms a firmer clot than that of venous blood. 



