22 



PRACTICAL PHYSIOLOGY 



vessels of the retina (p. 14) and draw your conclusions. Is it the front 

 layer of the retina or a back layer which is acted upon by light ? 



The following is another method of performing this experiment. 



Remove the objective from a microscope, arrange the mirror for 

 a good light and move the microscope from side to side ; a number 

 of vessels will be seen running vertically. The microscope is now 

 moved from before backwards until vessels are seen running 

 horizontally. Give the microscope a circular movement, the field 

 will be covered with vessels except in the direct line of vision in 

 which is a small area in which no vessels are seen, the macula lutea 

 or yellow spot. Make a diagram of the appearances in each case. 



Lesson III. To be provided for each pair of Students. 



1. An eye from an ox, [sheep or pig cleared of external tissues, fresh or 

 fixed for a day or two in formalin and then washed. A sharp razor. 

 2. Two or three ophthalmoscopes and the usual biconvex lenses. 3. A 

 model eye or the eye-piece of a microscope with a piece of paper fixed under 

 the lower lens with some prominent figure X or O marked upon it, the 

 whole fixed in a retort holder beside a suitable electric lamp. 4. Candle in 

 holder. 5. Convex lenses of different curvature. 6. Sheets of paper. 

 7. Needle in handle. 8. Pair of fine pointed compasses. 9. Millimetre 

 measure. 10. Card for astigmatism. 



To be provided for Class. 



1. Kuhne's artificial eye or some similar model. 2. Model of eye in orbit. 

 3. Microscopes with sections of (a) Anterior segment of eye with ciliary 

 processes ; (6) Posterior segment of eye with retina. 4. A small photo- 

 graphic camera. 5. Phakoscope. 



LESSON IV 



5. What Range of Objects can be seen at one Time ? The Field of 



Vision. 



METHOD. A. Black and White. 

 Describe a semicircle on a black- 

 board with the free ends of the 

 line finishing at one side. Mark 

 the centre of the circle at the 

 edge of the board and the middle 

 point in the circumference with 

 an X. This forms a rough " Peri- 

 meter." 



Keeping one eye closed, the 

 observer places his other eye at 

 the centre and directs it steadily 

 towards the middle point in the 

 circumference. A fellow student 

 slowly draws a piece of chalk 

 along the circumference from 

 below. The subject states when 



FIG. 16. To show the Field of 

 Vision in the vertical plane. 



(From No61 Paton's Essentials.) 



it becomes visible, and the other 

 marks this point. 



