Chemical Changes in Animal Organism. 305 



nected with the vessel H. The pump consists of a piston 

 and cylinder, the piston rod J being moved by a crank and 

 a connecting bar E. The pump is provided with cylinders 

 and pistons of varying diameters, so that it can be used 

 for organs of different sizes and varied rates of flow of the 

 blood. The volume of the blood delivered at each stroke 

 can also be varied by fixing the connecting bar E to 

 different points of the coned pulley G. The connecting 

 valves of the pump are rendered both gas and fluid tight 

 by inserting a double-convex lens into a piece of india- 

 rubber tubing which is thereby stretched, and allows gas 

 and fluid to pass in one direction, but not in the other. 

 The vessel H is connected with a large flask M, which in 

 its turn is connected with a mercury valve P and a mano- 

 meter R. The whipped blood of the animal is introduced 

 into the receiver A, and pumped into the main receiver H. 

 The mercury valve P is set at the required pressure, and 

 pumping is continued until air escapes through the valve, 

 so that blood in the receiver H is at the initial pressure 

 required for the perfusion. It is then passed through the 

 tube K to the arterial cannula through the organ, and 

 thence through the venous cannula to the vessel A. From 

 this it is pumped again into H, and this circulation can be 

 kept up continuously by means of a motor driving the 

 pump. The thrust of the pump and its rate are regulated, 

 so that enough air is pumped with the blood to aerate it 

 sufficiently. The air in excess of that required to maintain 

 the pressure at constant height passes through the vessel 

 M, and escapes through the mercury valve P. The vessel 

 M serves to collect the froth from the blood. 



The organs which have been chiefly employed for per- 

 fusion experiments are the heart and the liver. A large 

 variety of forms of apparatus for perfusion experiments 

 have been described, some of which are far more complex 



(1,997) 20 



