170 PHYSICAL EXPRESSION. 



are probably of frequent spontaneous occurrence, 

 and highly characteristic nerve-muscular postures. 



The application of the " principles of analysis " 

 may assist in determining whether a certain posture 

 observed is probably the outcome of the spontaneous 

 action of the nerve-centres. 



In these studies care must be taken to avoid 

 certain errors from attributing all postures to the 

 action of the central nerve-mechanism. 



Postures may be due to joint-disease, especially 

 arthritis deformans. M. Charcot carefully differen- 

 tiates between this deformity and the posture he 

 has described as the " writing hand " often seen .in 

 paralysis agitans. 



Postures may be due to local causes tumours, 

 inflammation, etc. 



Postures may be determined by organic condi- 

 tions, such as difficulties in the respiratory and 

 circulatory organs causing orthopnoea. Sir C. Bell 

 drew attention to this matter in his critical analysis 

 of the posture of the Dying Gladiator.* Such 

 postures are not the direct effect of the spontaneous 

 action of the nerve-centres. 



Gravity may be a factor in the causation of 

 postures, whether the member be "free" or 

 " engaged," thus : in the figure of Hercules at rest,t 

 he leans on a vertical club to support his body, 

 and the posture of the right arm is determined 

 mainly by gravity. In a paretic arm such as is 

 often seen in chorea, or from brain disease, the wrist 

 will droop into flexion if the forearm is held out 

 * See p. 303. t See p. 305. 



