290 



RESPIRATION 



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 centi- 

 meters per 100 c.c. of blood. 



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 figure 237. It con- 

 sists of two fixed glass globes, C and F, the 

 upper 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 pulley ; it also communi- 

 cates 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, 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 /, 

 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 



FIG. 237. Ludwig's Gas-pump. is similarly established in F; if G be now opened, 



the blood in I will begin 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 experiment several times the whole of the gases 

 of the specimen of blood is obtained, and may be estimated. 



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 



