CONTENTS. Xlil 



Ganglia. They are Reservoirs of Force. Summary of the Functions of the Sympathetic. 

 Illustration of the Sympathetic. The Abdominal Plexuses. 'The Solar Plexus. TheMesen- 

 teric Plexuses Page 333 



CHAPTER XVHI. 



OF THE VOICE. 



Origin of the Voice. Comparative Physiology of Noise, Song, Voice. Distinction between Song 

 and Speech. The Larynx, and its Action in Singing. Mutter's Explanation of the Action of 

 the Vocal Organs. Speaking Animals and Machines. 

 Nature of Words and their constituent Sounds. Vowels and Consonants. Whispering. Use 



of the Voice of Animals. 



Of Languages: their Duration, Character, History. Registry of Sounds by Writing and Print- 

 ing. Musical Signs. Alphabetic Writing 351 



CHAPTER XIX. 



OF HEARING. 



The Senses : General Remarks upon. Five Organs of Sense. Necessity of Apparatus for the 

 Appreciation of Time, Space, Pressure, Temperature, and Chemical Qualities. 



Of Hearing. General Structure of the Organ of Hearing. Physical Peculiarities of Sounds, In- 

 tensity, Time of Vibration, and Quality. The Tympanum, Cochlea, and Semicircular Canals 

 are for the Appreciation of these peculiarities. 



Structure and Functions of the Tympanum, or Measurement of Intensity. 



Structure of the Cochlea, its Spiral Lamina and Scalar. Measures the Time of Vibration. Ac- 

 complishment of Interference in the Scalce. Comparative Anatomy of the Cochlea. 



Structure of the Semicircular Canals. They estimate the Quality of Sounds. 



Comparative Anatomy of the Auditory Mechanism. Its Progress in Development. Imperfection 

 of the Doctrine of Means and Ends 359 



CHAPTER XX. 



OF VISION. 



Analogy between Sound and Light. Comparative Anatomy of Vision. Perception of Warmth. 

 Structure of Ocelli. Use of Lenses. Physical Principle of the Organ of Vision. 



Description of the Human Eye. Optical Action of its Parts. Spherical and Chromatic Aberra- 

 tion. Receiving Screen of the Eye is the black Pigment. Long and short Sight, and their 

 Correction. Limits of Vision are included in one Octave. Limit in estimating the Brightness 

 of Light. 



Nervous Mechanism of the Eye : its Structure and Functions. Manner of Perception by the 

 Retina. The black Pigment absorbs the Rays. Single and double Vision. Duration of Im- 

 pressions. Ocular Spectra. Erect Vision. Idea of the Solidity of Bodies. Hypothesis of 

 the Action of the Retina. 



Accessory Apparatus of the Eye. The Eyebrows. Eyelids. Lachrymal Apparatus. Muscles 

 of the Ball 379 



CHAPTER XXI. 

 OF CEREBRAL SIGHT OR INVERSE VISION. 



Difference between ordinary Vision and cerebral Sight. Inverse Vision depends on the Vestiges 

 of Impressions existing in the Brain. 



Condition of our perceiving these Impressions is that they must be equal in Intensity to present 

 Sensations. Two Methods of accomplishing this Equalization : 1st, by re-enforcing the old Im- 

 pressions ; 2d, by diminishing the present Sensations. 



Emergence of old Impressions in Sleep, Fever, Death. Artificial Emergence of such Vestiges by 

 Protoxide of Nitrogen, Opium, etc. 



Cerebral Sight used teleologically to indicate the Immortality of the Soul. 401 



