390 ELEMENTARY PHYSIOLOGY less. 



amply conscious of the failure, which we signify by the 

 word giddiness. This word is not always used in quite 

 the same sense. It will be worth while to inquire more 

 particularly what we mean by it. 



To take an instance, many persons, if they have to look 

 down from a considerable height, such as the edge of a 

 precipitous cliff, or the tower of a high building, or in some 

 cases even a scaffold, say tliey feel giddy. This feeling, 

 which it is difficult to describe, at all events involves the 

 inability to carry out or co-ordinate ordinary movements, 

 and would if strong enougli lead to complete collapse, in 

 which case the person would not only l)e unable to pro- 

 ceed but would actually fall. Again, if a person turns 

 round rapidly a few times and then stops he describes 

 himself as feeling giddy, but in this case he has a perfectly 

 definite sensation that the room is swinging round ; at the 

 same time if he tries to move his gait is unsteady, and if 

 he is giddy enough he falls down. 



The power of co-ordination of the muscles, which 

 enables the body to maintain its equilibrium, is the result 

 of sensations which come from more than one sense organ. 

 In the fii'st of the two instances of giddiness which have 

 been given, the cause of giddiness was in really a failure 

 of the sense of sight to adapt itself to unaccustomed 

 conditions ; indeed, in some persons the giddiness ex- 

 perienced in lofty positions is overcome by the adequate 

 use of glasses. The sense of sight is one of those which 

 contribute to the power of co-ordination. Sensations 

 which come from the limbs are also factors. This is 

 evident in the condition of persons stricken with locomotor 

 ataxy. The gait of one suffering from this malady is 

 extremely clumsy and unsteady, and, indeed, is only 

 possible because he can use his vision instead of the 

 sensations which, owing to the diseased condition of his 

 spinal cord, fail to come from his legs. He walks by 

 seeing a spot in front of him at a suitable distance and 

 planting his foot upon it ; blindfolded he would at once 



