PROBLEM 233 259 



Problem 232 : How to find out certain defects of vision in the 

 laboratory. 



Materials. — Schnellen's test cards, spectacles with diopter 

 lenses, clock dial chart. 



a. Test for Farsightedness 



Method. — Using the Schnellen's test cards, locate the finest 

 line that can be read at a distance of 20 feet. Test each eye 

 separately, covering the eye not in use with a piece of cardboard. 

 Then place a pair of spectacles with a 50 plus diopter lens before 

 the eyes. If as fine or a finer line can now be read, then far- 

 sightedness is present and an oculist should be consulted, espe- 

 cially if headaches or other symptoms of eye defects are present. 

 Farsightedness is one of the most frequent causes of eyestrain and 

 is hard to detect because the eyesight seems so good. 



b. Test for Nearsightedness 



Method. — Use the above-mentioned charts. Determine the 

 finest type you can read at a distance of 20 feet. If it is larger 

 than the 20/20 line, then your vision is defective and you should 

 probably consult an oculist, especially if you have any symptoms 

 of eyestrain. 



c. Test for Astigmatism 



Method. — Use the clock dial disk at 20 feet. If some lines are 

 blacker than others, then astigmatism is present. If headaches 

 or other symptoms are present, then you should consult an oculist 

 and have glasses fitted to correct this trouble. 



Next examine a chart or model of the human eye and deter- 

 mine what defects must occur within your eye to cause the defects 

 in vision you have found. (Your teacher will explain the terms 

 " nearsightedness, farsightedness, and astigmatism.") 



Conclusioii. — Have I any eye defects? If so, what are they, 

 and how must I go about to correct them? 



Problem, 233 : What are some of the effects of alcohol on the 

 nervous system ? 



Method. — Using the figures on pages 363, 365, 366, 369, 370, 371, 

 372, Civic Biology, make a graph to show the effect of alcohol upon 



