224 PRACTICAL PHYSIOLOGY 



EXPERIMENT I. Define an area of the skin, for example, on the 

 volar surface of the forearm, about 5 cms. square. Carefully work 

 over this area with a small camel's hair brush, 1 lightly touching 

 adjacent small areas and marking with coloured ink the places where 

 the contact is felt. The subject of the experiment should close his 

 eyes, the observer marking the spots according to the replies of the 

 subject. Instead of a camel's hair brush, a fine hair fixed to the end of 

 a match may be used. 



b. The sense of temperature. Bodies at a lower temperature than 

 the skin give a sensation of cold, at a higher temperature a sensation of 

 warmth. The distribution of these two senses of temperature is not 

 identical. 



EXPERIMENT II. The most convenient way of testing for cold or 

 warm spots is to take several soldering irons, the points of which have 

 been filed down to give a surface of about a square millimetre. These 

 are kept in water at the desired temperature till required. Or, a 

 hollow copper rod, through which a circulation of water at the desired 

 temperature is arranged, may be adopted. 



As in Experiment I. explore the defined area of skin for responses to 

 the different contacts in respect of heat or cold. The temperature 

 should not be extreme, about 10 above or below that of the surface of 

 the skin is sufficient. At extreme temperatures (e.g. 70 C.) other 

 sensations come into play. Mark out the distribution of heat and cold 

 spots in inks of colours different from that used in Experiment I. It 

 may be observed that the temperature spots are readily fatigued. 



c. The sense of pain. 



EXPERIMENT III. Some form of algometer is required for the 

 purpose of stimulation. Bristles, pointed with a razor, fixed in a light 

 wooden rod, an ordinary mounting needle, or perhaps best, a needle 

 fixed to the end of a bristle, are alternative forms of algometers. The 

 amount of pressure used is of consequence, and to keep this constant 

 the degree of bending of the bristle should not vary. Mark out the 

 pain spots with distinctive ink. 



It will be found in the above experiments that there is a lack of 

 identity in the spots, corresponding to the different sensations, but if 

 the marks be allowed to remain for some hours and again the sensations 

 are tested, there will be found no alteration of position. 



1 Such a brush should be *5 cm. in length and forming a bundle not more 

 than '05 cm. at the base. 



