148 THE tfEKVOUS SYSTEM. 



CHAPTER IX. 

 THE NERVOUS SYSTEM. 



Animal and Vegetative Functions Sensation, Motion, and Volition 

 The Structure of the Nervous System The White and Gray Sub- 

 stances The Brain Its Convolutions The Cerebellum The Spi- 

 nal Cord and f its System of Nerves The Anterior and Posterior 

 Roots The Sympathetic System of Nerves The Properties of Nerv- 

 ous Tissue Excitability of Nervous Tissues The Functions of the 

 Spinal Nerves and Cord The Direction of the Fibres of the Cord 

 Reflex Activity, and its Uses The Functions of the Medulla Oblon- 

 gata and the Cranial Ganglia The Reflex Action of the Brain. 



1. Animal Functions. The vital processes which we 

 have been considering, in the three previous chapters, of 

 digestion, circulation, and respiration belong to the class 

 of functions known as vegetative functions. That is, they 

 are common to vegetables as well as animals; for the 

 plant, like the animal, can originate nothing, not even 

 the smallest particle of matter; and yet it grows, blossoms, 

 and bears fruit, by reason of obtaining and digesting the 

 nutriment which the air and soil provide. The plant has 

 its circulatory fluid and channels, by which the nutriment 

 is distributed to all its parts. It has, also, a curious ap- 

 paratus in its foliage, by which it abstracts from the air 

 those gaseous elements so necessary to its support; and 

 thus it accomplishes vegetable respiration. These vege- 

 tative functions have their beginning and end within the 

 organism of the plant; and their object is the preservation 

 of the plant itself, as well as of the entire species. 



2. The animal, in addition to these vegetative functions, 

 has another set of powers, by the use of which he becomes 

 conscious of a world external to himself, and brings him- 



1. What processes are known as the vegetative functions? Why so called? 

 What properties and functions does the plant possess ? Their object ? 



2. What second set of powers has the animal ? What functions are mentioned ': 

 The advantage they give ? 



