THE RESPIRATORY CHANGES IN THE BLOOD. 



347 



municate by means of air-tight stopcocks alternately with a receiver containing the 

 blood and with a receiver to collect the gas. When the movable globe filled 

 with mercury is raised above the fixed one, the mercury from the former runs 



FIG. 92. 



Diagrammatic illustration of Ludwig's Mercurial Gas-pump : A and B are two glass globes con- 

 nected by strong India-rubber tubes, a and 6, with two similar glass globes, ^1'and B'. A is further 

 connected by means of the stopcock c with the receiver C containing the blood (or other fluid) to 

 be analyzed, and B by means of the stopcock d and the tube e with the receiver D for receiving the 

 gases. A and B are also connected with each other by means of the stopcocks/ and g, the latter 

 being so arranged that B also communicates with B' by the passage g'. A' and B' being full of 

 mercury, and the cocks k,f, g, and d being open, but c and g' closed, on raising A' by means of the 

 pulley p the mercury of A' fills A, driving out the air contained in it into B, and so out through 

 e. When the mercury has risen above g,f is closed, and g f being opened, B' is in turn raised 

 until B is completely filled with mercury, all the air previously in it being driven out through 

 e. Upon closing d and lowering B' the whole of the mercury in B falls in B', and a vacuum con- 

 sequently is established in B. On closing g', but opening g,f, and k, and lowering A', a vacuum 

 . is similarly established in A and in the junction between A and B. If the cock c be now opened, 

 the gases of the blood in C escape into the vacuum of A and B. By raising A' after the closure 

 of c and opening of d, the gases so set free are driven from A into B, and by the raising of B' 

 from B, through e into the receiver D, standing over mercury. 



into and completely fills the latter, the air previously present being driven out. 

 After adjusting the C9cks, the movable globe is then depressed thirty inches 

 below the fixed one, in which the consequent fall of the mercury produces an 

 almost complete vacuum. By turning the proper cock this vacuum is put into 



