THE BLOOD. 155 



consider here its general properties. It is a stringy elastic substance 

 belonging to the proteid class of bodies. Blood contains only -.2 per 

 cent of fibrin. It can be converted by the gastric or pancreatic juice 

 into peptone. It possesses the power of liberating the oxygen from 

 solutions of hydric peroxide H 2 2 or ozonic ether. This may be shown 

 by dipping a few shreds of fibrin in tincture of guaiacum, and then 

 immersing them in a solution of hydric peroxide. The fibrin becomes 

 of a bluish color, from its having liberated from the solution oxygen, 

 which oxidizes the resin of guaiacum contained in the tincture, and 

 thus produces the coloration. 



The Gases of the Blood. 



The gases contained in the blood are carbonic acid, oxygen, and ni- 

 trogen, 100 volumes of blood containing from 50 to 60 volumes of these 

 gases collectively. 



Arterial blood contains relatively more oxygen and less carbonic acid 

 than venous. But the absolute quantity of carbonic acid is in both 

 kinds of blood greater than that of the oxygen. 



Oxygen. Carbonic Acid. Nitrogen. 



Arterial Blood . . 20 vol. per cent. 39 vol. per cent. 1 to 2 vols. 



Venous " 



(from muscles at rest) 8 to 12 " " 46 " " 1 to 2 vols. 



The Extraction of the Gases from the Blood. As the ordinary air pumps are 

 not sufficiently powerful for the purpose, the extraction of the gases from the 

 blood is accomplished by means of a mercurial air-pump, of which there are 

 many varieties, those of Ludwig, Alvergnidt, Geissler, and Sprengel being the 

 chief. The principle of action in all is much the same. Ludwig's pump, 

 which may be taken as a type, is represented in fig. 134. It consists of two 

 fixed glass globes, C and F, the upper one communicating by means of the 

 stop-cock D, and a stout india-rubber tube with another glass globe, L, which 

 can be raised or lowered by means of a pulley ; it also communicates by means 

 of a stop-cock, B, and a -bent glass tube, A, with a gas receiver (not repre- 

 sented in the figure) , A, dipping into a bowl of mercury, so that the gas may 

 be received over mercury. .The lower globe, F, communicates with C by 

 means of the stop-cock, E, with I in which the blood is contained by the stop- 

 cock, G, and with a movable glass globe, M, similar to L, by means of the 

 stopcock, H, and the stout india-rubber tube, K. 



In order to work the pump, L and M are filled with mercury, the blood from 

 which the gases are to be extracted is placed in the bulb I, the stopcocks, H, 

 E, D, and B, being open, and G closed. M is raised by means of the pulley 

 until F is full of mercury, and the air is driven out. E is then closed, and 

 L is raised so that C becomes full of mercury, and the air driven off. B is 

 then closed. On lowering L the mercury runs into it from C, and a vacuum 

 is established in C. On opening E and lowering M, a vacuum is similarly 

 established in F; if G be now opened, the blood in /will enter ebullition, and 

 the gases will pass off into F and C, and on raising M and then L, the stopcock 

 B being opened, the gas is driven through A, and is received into the receiver 



