208 SPECIAL PHYSIOLOGY 



other pithed frogs in the mean time. The number of seconds re- 

 quired for response may be counted from a metronome or from a 

 watch. 



Latent periods in seconds. 



Strength of stimulus. , ' > 



Frog A. Frog B. 



H 2 SO 4 0.05 per cent t 



H 2 SO 4 0.1 " " 



H 2 SO 4 0.2 " " 



H 2 S0 4 0.3 " " 



H 2 S0 4 0.4 " < 



(14) THE IRRADIATION OF REFLEX ACTION. In the above- 

 described experiment it will probably have been noted that the 

 stronger the stimulus the more extended the response i. e., the 

 greater the number of muscles brought into action. 



When only the tip of the toe is touched to very weak acid the 

 response will be a simple flexion of the tarsus, and this only after 

 several seconds. When stronger acid is applied to the toe or web 

 the crus and the femur may both be flexed, and the action is some- 

 times repeated. 



Repeat some of the experiments, paying special attention to the 

 variation of extent of response, with varying strength of stimulus. 



Note that in some cases the response involves the opposite side, 

 as well as higher and lower levels of the cord. 



(15) LOCATION OF REFLEX CENTERS. Take one of the pithed 

 frogs that has been responding typically. Run a pithing probe down 

 the spinal canal, thus functionally destroying the spinal cord. 



Apply any of the stimuli mentioned above. Note results, and 

 account for same. 



II. REFLEXES IN THE HUMAN SUBJECT. 



Until one's attention is called to it, he is likely to overlook the 

 great importance of reflex action and the reflexes in the mainte- 

 nance of the human body. The eyes are protected from dust and 

 other irritable substances, the lungs from dust and irrespirable 

 gases, through the intervention of reflex action. The food is moist- 

 ened and the digestive juices started through reflex response to the 

 stimulating influence of food in the mouth and digestive canal. The 

 respiration, circulation, heat regulation, excretion, and various other 

 vital processes are controlled through reflexes. The paramount im- 

 portance of reflex action thus becomes apparent. 



A disturbance of certain reflexes becomes a clinical symptom of 

 considerable importance. 



It is proposed here to study briefly a few of these reflexes. Their 

 detailed discussion is left to the text-books. 



