408 ELEMENTARY PHYSIOLOGY less. 



near objects, during deep sleep, or after the administration 

 of morphia and several otlier poisons, and in the early 

 stages of the action of alcohol and cliloroform. On the 

 other hand the pupil is dilated when the eye is accommo- 

 dated for distant objects, during violent muscular activity, 

 during dyspnea, after the ailministi'ation of atropine 

 and some other poisons, and in the later stages of the 

 action of alcohol and cliloroform. 



In the case of the action of many poisons the effect 

 produced is due, notably in respect of atropine, to a purely 

 local action on the circular (sphincter) fibres of the iris, or 

 on the endings of the nerves in these fibres. 



Rays of light passing into the eye undergo a bending or 

 refraction (i) as they enter tlie eye, at the surface of the 

 cornea, (ii) as they pass tlirough the lens ; and as a 



Fig. 129. — The Formation of an Image on the Retina. 



result of this action of the cornea and lens an image of 

 any object in the external world is formed on the retina. 



In the water camera the image brought to a focus on 

 the screen at the back is inverted ; the image of a tree for 

 instance is seen with the roots upwards and the leaves and 

 branches hanging downwards. The right of the image 

 also cori'esponds with the left of the object and vice versa. 

 Exactly the same thing takes place in the eye with the 

 image focussed on the retina. It too is inverted. This 

 fact often gives rise to the question, Why then do Ave see 

 objects in the external world in an erect position and not 



