CHAPTER VI 



Model of the Circulation. Prepare with glass and rubber tubing, etc., 

 an arrangement such as that indicated in Fig. 20. A is the bulb 

 of a Higginson syringe, to be obtained from the druggist, the valves 

 being removed. At one end a valve B is connected. This consists 

 of a glass tube, represented separately at M, closed at one end, and 

 having a hole blown in the side about 2 cm. from the closed end. 

 The edges of this hole are smoothed in the flame. This is pushed 

 through a rubber cork fitting the end of a wider tube, which is 

 drawn out at the other end to fit f^- in. soft rubber tubing. A piece 

 of sheet rubber is tied over the hole, with its free edges just meet- 

 ing opposite the hole, the threads being in the situations represented. 

 When water is pressed through this valve it escapes between the 

 rubber and the cork. Any pressure in the opposite direction closes 

 the hole by forcing the rubber into it. The bulb with its two 

 valves represents the heart. D is a mercury manometer connected 

 by a T-tube in the course of the current. This T-tube is continued 

 by a 4-ft. length of y\ in. rubber tubing (c), of moderately thin 

 walls, representing the arterial system. E is a screw pinchcock to 

 represent peripheral resistance. F is a wide glass tube, fitted with 

 rubber corks through which short glass tubes pass, and filled with 

 small pieces of sponge, loosely packed. This represents the 

 capillaries. A short rubber tube connects this with a 6-in. length 

 of the inner tube of a bicycle tyre (G), which has rubber corks 

 similar to those of F. There is another mercury manometer (H) to 

 indicate the pressure in the veins, which are represented by that 

 part of the model between F and K. K is a valve similar to B, and 

 represents the mitral valve of the heart, whereas B represents the 

 aortic valves. K is, of course, connected in such a way that water 

 can pass it from the vein to the bulb and not the opposite way. 

 G and K are connected by a short piece of rubber tubing, so that 

 they can be disconnected for convenience of filling the system with 

 water. L is a T-tube joined to a funnel, for the purpose of running 

 in more water. It is closed by a pinchcock. 



With this schema a large number of instructive experiments can 

 be performed. The following are some of these : 



Disconnect the tube C from F, and G from K. Insert a glass 



218 



