in their Structure and Functions, 29 



hop plant, turning round a pole, follows the course of the sun 

 from east to west : these are all examples of instinct. 



I have now endeavoured to prove that a muscular tissue 

 exists in vegetables as well as animals. My next object will 

 be to show that plants likewise possess a nervous tissue. In 

 doing this, I am not unconscious upon what very debatable 

 ground I am entering. At the same time, I must confess 

 that the facts which the researches of physiologists have dis- 

 covered render it more than probable that plants are endued 

 with nerves. The nervous system, as it is found in man and 

 the higher classes of animals, consists of the brain, the spinal 

 cord, the ganglia, and the nerves. The brain is enveloped 

 in three distinct membranes, and is encased in the bones of 

 the cranium. The spinal cord, which is merely a prolonga- 

 tion of the brain, is also enclosed in a strong membranous 

 covering, and is lodged within the cavity of the backbone. 

 The nerves are small white medullary cords, which take their 

 origin from the lower surface of the brain and from the lateral 

 parts of the spinal cord. They pass out through apertures 

 at the bottom of the skull and sides of the vertebrae, and are 

 ramified over every part of the body. The ganglia are found 

 in various parts of the nervous system. They resemble little 

 brains, and are supposed to be sources of nervous energy. 

 In many of the lower animals, as worms and insects, no brain 

 is to be found, but only one or two longitudinal nerves placed 

 in the centre of their bodies, having attached to them, at 

 various distances, minute ganglia from which fresh ramifica- 

 tions of nerves proceed. The faculty which the nervous 

 system exercises, is to receive and transmit the impressions of 

 external objects to the brain; where they may be rendered 

 sensible to the mind, giving rise to what are denominated 

 perceptions. This faculty is called sensibility, and it possesses 

 two distinct modes of operation. The one is produced by 

 external impressions, which are conveyed by the media 

 [means] of the nerves to the brain ; the other is derived from 

 some change being generated in the brain itself, which is 

 transmitted along the nerves to some of the corporeal organs. 

 This latter constitutes volition. Notwithstanding, however, that 

 nervous action is often succeeded by perception, yet there are 

 many cases in which impressions never become perceptible 

 to the mind : in other words, sensation is generally attended 

 with consciousness ; but it may exist without it. For example, 

 whenever the nerves of any of the external senses are acted 

 upon by their appropriate stimuli, as, for instance, when light 

 is applied to the eye, we are conscious of the impression ; but 

 when food is taken into the stomach, we feel no impression 

 or sensation at all ; and yet we know that the stomach is as 



