RESPIRATION 



itself. The blood is a mass of corpuscles floating in the fluid plasma. An 

 analysis of the blood shows that it contains oxygen, carbon dioxide, and 

 nitrogen, the gases of the air. The usual method is completely to extract 

 the blood gases by an air-pump, figure 237, and determine the quantities in 

 cubic centimeters per 100 c.c. of blood. 



The Extraction of the Gases from the Blood. As the ordinary air-pumps are not suf- 

 ficiently 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 figure 237. 



It consists of two fixed glass globes, C and F, the up- 

 per one communicating by means of the stopcock, D, 

 and a stout India-rubber tube with another glass globe, 

 L, which can be raised or lowered by means of a pul- 

 ley; it also communicates by means of a stopcock, 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 

 stopcock, E, with / in which the blood is contained by 

 the stopcock, G, and with a movable glass globe, M y 

 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 ire to 

 be extracted is placed in the bulb 7, 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 7 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 over mercury. By repeating the ex- 

 periment several times the whole of the gases of the 

 specimen of blood is obtained, and may be estimated. 



FIG. 237. Ludwig's Gas -pump. 



Pfluger's analysis of the arterial blood of 

 the dog gave the following volumes per cent: 

 oxygen 22.6, carbon dioxide 34.3, and nitrogen 

 1.8. The analysis for the venous blood gives 

 a very much lower oxygen and a higher carbon dioxide per cent. The 

 average oxygen content of venous blood is 10 to 12 per cent and the carbon 

 dioxide 45 per cent. The blood in different veins of the body varies within 

 wide limits as regards its gas content. 



Oxygen. 



100 c.c. Arterial blood 22.6 c.c. 



100 c.c. Venous blood 12. c.c. 



Carbon 



Dioxide. 



34 C.C. 



45 c - c - 



Nitrogen. 

 1.7 c.c. 

 1.7 c.c. 



