The Special Senses 273 



ADDITIONAL EXPERIMENTS 



Experiment 126. Use a small pair of wooden compasses, or an 

 ordinary pair of dividers with their points guarded by a small piece of 

 cork. Apply the points of the compasses lightly and simultaneously 

 to different parts of the body and ascertain at what distance apart the 

 points are felt as two. The following is the order of sensibility : tip 

 of tongue, tip of the middle finger, palm, forehead, and back of hand. 



Experiment 127. By means of a spray producer spray the back 

 of the hand with ether and observe how the sensibility is deadened. 



Experiment 128. Generally speaking, the sensation of touch is 

 referred to the cutaneous surfaces. In certain cases, however, it is 

 referred even beyond this. Holding firmly in one hand a cane or a 

 pencil, touch an object therewith ; the sensation is referred to the 

 extremity of the cane or pencil. If, however, the cane or pencil be 

 held loosely in one's hand, one experiences two sensations : one cor- 

 responding to the object touched, and the other due to the contact 

 of the rod with the skin. 



Experiment 129. Wipe the tongue dry and lay on its tip a crystal 

 of sugar. It is not tasted until it is dissolved. 



Apply a crystal of sugar to the tip, and another to the back of the 

 tongue. The sweet taste is more pronounced at the tip. 



Experiment 130. Prepare a strong solution of sulphate of qui- 

 nine with the aid of a little sulphuric acid to dissolve it (bitter), a 

 5 per-cent solution of sugar (sweet), a 10 per : cent solution of com- 

 mon salt (saline), and a I per-cent solution of acetic acid (acid). 

 Repeat the process in Experiment 129 with sulphate of quinine in 

 solution. It is scarcely tasted at the tip, but is tasted immediately 

 on the back part of the tongue. 



Test in the same way the places in which the salines and acids are 

 tasted most acutely. 



Experiment 131. To illustrate the mtiscular sense. Take two 

 equal iron or lead weights ; heat one and leave the other cold. The 

 cold weight will feel the heavier. 



Experiment 132. Place a thin disk of cold\v&&, the size of a silver 

 dollar, on the forehead of a person whose eyes are closed ; remove the 

 disk, and on the same spot place two warm disks of equal size. The 



