THE NERVES. 97 



pulses : they control nutrition (trophic nerves) and secretion 

 (secretory nerves), and they may also increase or check other 

 efferent impulses. 



What is the velocity of the transmission of impulses ? 



Efferent impulses are somewhat slower than afferent, the rate 

 for the former being about 110 feet' per second, for the latter 

 about 150 feet. 



What are " personal error " and " personal equation " ? 



The time occupied in executing a voluntary movement at a given 

 signal for instance, the recording the time of a transit in an astro- 

 nomical observation is found to be sufficient to demand a correction 

 for an accurate result. This amounts to 1 to ^ of one second with 

 different individuals. The time lost in this way is known as the 

 personal error of the observer. When this has been ascertained 

 by experiment, the allowance to be made for the personal error is 

 his personal equation. This remains nearly constant for each 

 person. 



How do the sensory nerves terminate at the periphery? 



The sensory nerves ending in the skin find their way to certain 

 bodies (sense-organs) which are essential to the conduction of the 

 sensory impression to the central nerve-ending. These sense- 

 organs are of several kinds. In the fingers and toes are found 

 two kinds of sense-organs which may be especially mentioned : 

 1, touch-corpuscles; 2, Pacinian corpuscles. The anatomy and 

 physiological use of these bodies are still somewhat obscure ; 

 and, indeed, the whole subject of sensory nerve-terminations is 

 but illy understood. We may regard the fibres of sensory nerves, 

 as a majority, to form a minute plexus in the corium and to ter- 

 minate in sense-organs in a way not known. Some of the special 

 sense-organs are possessed of nerve-endings which are more clearly 

 observed. 



What two sets or systems of nerves do we possess ? 

 The cerebro-spinal and sympathetic. 



What constitutes the cerebro-spinal system? 



The brain, the medulla oblongata, and the spinal cord, with the 

 nerves proceeding from them. 



What constitutes the sympathetic system? 



Primarily, the sympathetic system consists of a double chain of 

 7 Phy. 



