QUESTIONS 193 



substance containing 4 per cent, phosphorus. When decomposed 

 by the action of alkalies it yields glycerophosphoric acid, cho- 

 lin (C 5 H 15 NO 2 ), and fatty acids such as oleic, palmitic, and 

 stearic. This decomposition occurs in the body when nerves 

 undergo degeneration. Cholin has been found in the liquids 

 of the body in the case of degenerative diseases of the nervous 

 system. Cholesterin (C 27 H 46 O) is widely distributed among the 

 tissues of the body, and is found especially in the white matter 

 of the nerves. Lecithin and cholesterin usually occur together, 

 and it is a most interesting fact that cholesterin antagonizes 

 lecithin in the activation of cobra venom. The cerebrosides 

 contain nitrogen but no phosphorus. They are found in myelin 

 in combination with lecithin. They belong to the group of 

 glucosides, for on hydrolytic decomposition they give rise to 

 the carbohydrate group, galactose. 



QUESTIONS ON CHAPTER XI 



What is a nerve-muscle preparation? 



Define a stimulus. How many classes are there? 



Upon what factors do the results of stimulation depend? 



Why is an electrical stimulus usually a desirable one? 



Distinguish between voltaic an'd induced currents. 



Define opening and closing shocks. Which is the stronger? 



Tell why the breaking induced current is stronger than the making. 



What are subminimal and supermaximal stimuli? 



What changes take place in the contraction of a muscle as the excitation 

 increases in strength? 



What is Du Bois-Reymond's law? 



Illustrate how density of current affects its exciting power. 



Discuss the results of duration of stimulus. 



What are ascending and descending currents? 



Discuss changes in irritability and conductivity of a nerve during electro- 

 tonus. 



What are anelectrotonus and katelectrotonus? 



What is the relation of rise of irritability to excitation? 



Discuss in detail Pfliiger's law. 



At what points may an impulse be generated when a nerve in situ is 

 subjected to a constant current? 



In what order do the contractions occur as the strength of current is 

 increased? Give reasons. 



What is meant by the "reaction of degeneration?" 



Upon what factors does the irritability of a preparation depend? 



Discuss the effect of changes in environment upon the irritability of 

 tissue. 



Discuss the effect of severing a nerve fiber from its cell body. 



How does functional activity alter irritability? 



Distinguish between fatigue and exhaustion. 



Give proof that waste products are formed during activity. 

 13 



