LABORATORY MANUAL OF PHYSIOLOGY. 



forks, the time-marking lever may be caused to vibrate any desired 

 number of times per second. 



The number of interruptions is varied until a frequency is ob- 

 tained which shuts off the light in such a manner that the cilia 

 appear stationary. This frequency corresponds to the rate of vi- 

 bration of the cilia. 



3. Pith a Frog. This, ordinarily, means destroying the brain, 

 and is accomplished in the following manner: Hold the frog in the 

 left hand, securing the head between the index and middle fingers, 

 with the thumb over the back. Bend the head forward so as to 

 place the occipito-atlantal ligament on the stretch and expose the 

 articulation between* the skull and the vertebral column. With 

 fine scalpel or fine pointed scissors, make an incision through the 

 neuraxis at this point. Run a blunt-pointed seeker through this 

 opening into the cranial cavity and destroy the brain. If required, 

 the cord may be broken up in a similar manner. 



(a) With heavy scissors, cut off the lower jaw of the frog. Place 

 the frog on its back ; wash off the mucous membrane of the roof of 

 the mouth with normal salt solution ; remove the excess with filter 

 paper; place a small piece of cork on the mucous membrane near 

 the apex of the jaw and watch its movement. Time the movement 

 of the cork for a certain distance. 



(b) Repeat the experiment after having bathed the mucous 

 membrane with warm salt solution (36 C.). 



(c) Repeat again after bathing with cold salt solution (5-10 C.). 

 What is the effect of temperature upon ciliary motion ? 



(d) The above experiment may be repeated, using the appa- 

 ratus shown in Fig. 5. For this purpose, dissect out a piece of 

 the frog's oesophagus; pin it, outer side down, upon a cork board; 

 adjust the weight (W) and the lever (P) so that the rate of ciliary 

 movement may be indicated on the graduated arc (S). 



(e) Using the same apparatus, try the effect of various weights 

 upon the ciliary motion, beginning with five grams and increasing 

 the weight until the cilia are no longer able to move it. 



(/) Repeat this experiment with a fresh preparation, tilting the 



[W] 



