PROBLK.M 2:V.] 250 



Problem V/iV ; Ifow to find out cerfnin t/cfcrfs of vision in the 

 laboratory. 



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

 lenses, clock dial chart. 



a. Test for Farsightedness 



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

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

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

 Then place a pah' of spectacles witli a 50 phis diopter lens before 

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

 sightedness is present and an oculist should ])e 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 an>- 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 tlu^ human eye and deter- 

 mine what defects must occur within yoiu- eye to cause the defects 

 in vision you have found. (Your teacher will I'xplain the terms 

 '' nearsightedness, farsightedness, and astigmatism.") 



Conclusion. — Have I anv eve defects? If so. what are ihfv, 

 and how nmst I go about to correct them? 



Problem 23:i : What are some of the efferts of aJrohol on the 

 nervous system ? 



Method. — Using the figures on pages 'MY.], 305, 300, 30i). :>70. 37 1 . 

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



