180 



ADVANCED LESSONS IN PRACTICAL PHYSIOLOGY 



ones, the right anterior and left posterior, and the left anterior and 

 right posterior. 



Identify the ampulla of each canal and determine its position. Tilt 

 the skull in different directions, and state which canals are involved in 

 any particular movement. 



3. Model Illustrating the Action of the Semicircular Canals. 

 Secure a model, such as is represented in Fig. 106. Rotate the circular 

 glass tube containing water. Observe that the tube moves first and 

 that at this time the water is still stationary The bristles, representing 

 the hair processes of the cells lining the ampulla, are deviated against 

 the direction of the rotation. Presently the water will move with 

 practically the same velocity as the tube. The hair processes then 

 extend straight into the fluid. On stopping the tube the water will 

 continue to move onward, deviating the hair processes in the direction 

 of its flow. 



FIG. 106. DIAGRAMMATIC REPRESENTATION OF A MODEL ILLUSTRATING THE DEVIATION 



OF THE HAIR PROCESSES OF THE AMPULLA. 



D, Disk rotated by hand; T, circular glass tube filled with water; B, bulbular enlargement 

 containing a long camel's-hair brush, vertically placed. 



While a free movement of the endolymph is not possible, this schema 

 illustrates at least the principle involved in the activation of the hair cells. 



4. Acuity of the Dynamic Sense. Sit upon a revolving chair. Close 

 your eyes and lift the feet from the floor. Instruct the assistant to 

 turn the chair a short distance. What canals are involved in this 

 movement? Determine the number of degrees through which the rota- 

 tion has taken place. Ascertain the least possible rotation which will 

 impart a sensation of movement. How would you rate the acuity of 

 this sense? 



Bend your head forward. Repeat these tests. What canals are 

 involved in this position? Is the sensitiveness of these canals toward 

 this particular movement greater or slighter than that of the horizontal 

 canals? 



5. Rotation Effects in Mammals. Place a rabbit in a long and 

 narrow box which may be rotated around its vertical axis. Revolve 

 the. box at a moderate speed about ten times around its axis. Imme- 

 diately tilt the box so that the rabbit slides out upon the table. Observe 



