82 PERSONAL APPEARANCES IN HEALTH AND DISEASE. 



minutes, and then the two hands compared, the one will 

 look pale and white, the other flushed and red. The first 

 is white, because by holding it up the return of blood from 

 it by the veins has been aided by the action of gravity; in 

 the other it has been retarded for the same reason. Thus 

 temporarily there has been produced a condition of com- 

 parative bloodlessness or anczmia in the one hand, and a 

 condition of plethora or congestion (hypercemia) in the 

 vessels of the other. The experiment may be varied by 

 pressing out the blood from one hand, when you will get a 

 white spot where the pressure was applied, and conversely, 

 if the part be rubbed violently, it becomes red and warm. 

 The reason of the pallor in the first instance is obvious 

 enough, the pressure squeezes the blood out of the 

 vessels of the part. The reason of the redness in the 

 latter example is not so obvious, and requires a little 

 further explanation. All the blood-vessels, the arteries 

 more particularly, have muscular walls, which can contract 

 when the nerves which go to them are irritated, just as 

 the muscles of the arms contract if the nerves going to 

 them be stimulated, as they always are when by an act 

 of the will the brain sends its message down them to 

 exert a particular movement. The modus operandi 

 however in connection with the blood-vessels is different 

 from that of the muscles of the arm, or any of those 

 which are under the control of the will ; for the muscular 



