PHYSIOLOGICAL DEMONSTRATION 



231 



of these is placed a representation of the heart, as at A (fig. 

 118), showing the ventricles and auricles, while the moving 

 slide B, actuated by the winch K, occupies the other. This 

 latter slide consists first of the foundation design shown in B, 

 on which is painted in black ground a scheme of the distribu- 

 tion of blood in the human body, as seen enlarged in fig. 119. 

 The portion a shows the circulation in the upper extremities, 

 head, and lungs ; b that of the intestines and lower extremities. 



b 



FIG. 118. Mechanical Slide for showing Circulation 



The black space 1, 2, 3, 4 in B is filled by the picture of the 

 heart in A, so that the points shown by 1 , 2, 3,4 coincide ; 

 thus the two together make up the whole figure 119. The 

 glass on which B is painted should be very thin. The 

 movable portion of the slide is shown at C, and consists 

 of the three toothed wheels a', h, and b', filled with glass. 

 On a' are drawn many radial lines halfway from circumference 

 to centre, and on h similar radial lines from the centre half- 



