160 ADVANCED LESSONS IN PRACTICAL PHYSIOLOGY 



A simple secretory reflex may be produced by moistening the 

 mucous lining of the mouth with a few drops of very dilute acetic acid 

 or by chewing a piece of rubber or paraffin. 



The sneezing reflex may be elicited by touching the mucous lining 

 of the nasal cavity with a few cotton fibers. Inhibit this reflex by 

 pressing upon the upper lip with the index-finger. 



4. Tendon Reflexes in Man. Cross your legs, allowing one leg to 

 hang perfectly free. Let the assistant strike the patellar ligament of 

 the free leg with the outer margin of his hand. Note the contraction 

 of the quadriceps muscle and the upward kick of the leg and foot. 

 During this test the subject should be perfectly inattentive, otherwise 

 cerebral inhibition will result. 



"Interlock the index-fingers of your hands. While you make a forced 

 effort to separate these fingers let the assistant elicit the patellar reflex. 

 Note that the kick is now much stronger than before (reinforcement of 

 reflexes) . Explain . 



Stand beside a low chair with your leg resting upon it. Let the 

 assistant strike the tendo achillis. The foot will be extended, owing to 

 the contraction of the gastrocnemius muscle. 



While the ankle-clonus is not observed in healthy persons, the 

 student should familiarize himself with the method employed in eliciting 

 it. The patient is seated and rests his leg upon a chair of equal height, 

 allowing the foot to project beyond its edge. Steady the leg with your 

 left hand and with your right hand suddenly flex the foot upon the leg, 

 so as to put the tendo achillis on the stretch. A series of clonic con- 

 tractions of the corresponding muscles will resulMn persons afflicted 

 with certain spinal diseases. 



Another peculiar phenomenon noted in certain spinal diseases is 

 the so-called Babinski phenomenon. Under normal conditions the 

 tickling of the sole of the foot results in a flexion of the toes upon the 

 foot (plantar reflex), whereas under certain abnormal circumstances the 

 first toe may be extended and the others flexed. 



5. Muscle Tonus. Etherize a frog under a bell-jar. When all 

 sensibility has been lost, open the abdomen. Place the sciatic nerve of 

 one side in a loose ligature. Suspend the frog in the usual way. Note 

 that the legs are held in a position intermediate between complete re- 

 laxation and contraction (tonus). Divide the sciatic nerve previously 

 placed in the ligature. Observe that the corresponding leg now assumes 

 a more dependent position, i. e., relaxes more completely. 



Remove the skin from the normal leg, and again note the position 

 of this leg. It will now assume the level of the opposite leg, the sciatic 

 nerve of which has been divided. Explain this result, making use of 

 the contention that the tonus of skeletal muscles is dependent upon 

 afferent stimuli derived from the integument. 



6. Threshold of Stimulation. Pith a frog. Carefully expose one 

 sciatic nerve in the thigh. Determine the least strength of tetanizing 

 current which will cause a spreading of reflexes when applied to the skin 



