380 PHYSIOLOGY AND HEAXTII. 



or all of the other organs may derange the nervous system, 

 and produce mental derangement. It is also manifest that 

 the abuse or neglect of any of the passions, propensities, or 

 mental faculties, may produce the same result, in greater or 

 less degree, of disordered mind. Most, if not all the causes 

 of partial or total insanity, come within our cognizance, and 

 are originally within our control. The brain and the mind 

 are as subject to fixed laws as the other organs, and it is left 

 for us to see that the conditions of their life are fulfilled, 

 and that we enjoy, not only general and open mental health, 

 but, under every circumstance, and in every moment of our 

 lives, in secret as well as in public, we possess full mental 

 strength, and the clearest power of thought, and the most 

 perfect control over our feelings and passions. 



EYE. 

 CHAPTER XVI. 



Eye. Situation. Composition. Humors. Lens. Coverings. 

 Iris. Pupil. Effect of Light. Lids. Tears. Lachrymal 

 Apparatus. Muscles. Cross-eye. Optic Nerve. 



884. The eye is placed in a deep, bony socket in the skull. 

 This socket extends far backward at the base of the brain, 

 and defends this tender organ from blows and accidents on 

 every side except the front. 



885. The eyeball is composed of three substances. 



The aqueous, or watery humor, (Fig. LXVI. b,} is a clear, 

 transparent fluid, and stands in the front of the eye. 



The vitreous humor forms almost the whole of the globe, 

 (Fig. LXVI. d.) This is a transparent substance, and soft like 

 a jelly. It is enclosed in a very delicate membrane, which 

 covers its outside, and, extending through it, forms many 

 cells, which contain this humor. 



