319 

 Sound tests. 



In a quiet room tlie ticking of an electric bell was deadened, 

 by distance and by wrapping the bell in a box with cotton- 

 wool, to such a degree that the intensity of the sound was 

 only just abo\'e the border value. On the table in front of the 

 subject, who regidarly heai'd the ticking, there was a hubbub-maker 

 of Barany, which could be set going automatically through an electric 

 contact, immediately aftei' each tick. By having observations 

 made after the tick, with and without subsequent noise in irregular 

 oi'der, it can precisely be determined how often the weak impulse 

 is lost by the retrograde power of the stj-onger noise. 



In thirteen normal persons nnd in thi-ee suffering from dementia 

 (2 dem. paralytica and 1 dem. arteriosclerotica) twenty tests were 

 made daily on each [)erson during five days. 



Average number of observations. 



Number 



Without subsequent 

 strong sound. 



With subsequent 

 strong sound. 



Normal 

 Dement 



13 

 3 



97.1 

 50.0 



88.9 

 



The great disturbances in the observation and the enormous 

 destruction in the sufferers from dementia are immediately ai)parent. 



Touch tests. 



It can be easily verified that the observation of a slight rough- 

 ness, which one feels by stroking the fingers ovei- a flat suiface, 

 disappears when the observation is followed by a strong touch 

 impulse. It is not necessary that the strong subsequent impnlse 

 should act on the same locality, but the preceding weak observation 

 also disappears if the subsequent strong inipidse acts on anolhei- 

 part of the finger, or even when it acts on one of the fingers of 

 the other hand. 



Tests were put in the following way, on one half of a smooth 

 disc a layer of paper 3 mm. thick was pasted. When the disc 

 revolves swiftly, the fingej-s, i-esting on the disc, clearly feel the 

 unevenness. If now a larger elevation is plac(Ml at some distance 

 from this unevenness so that the finger will collide with this eleva- 

 tion during the revolution, after it has passed the smaller uneven- 



21*. 



