Psychic Distuyhauccs ; Motor Disturbances. 427 



in animals, especiall}- by the group of symptoms known as 

 ''licking" or pica (wool-eating sheep), the animals showing 

 an inexpressible desire to lick all sorts of objects, even nauseat- 

 ing substances, and to eat them ; an ultimately fatal cachexia 

 developing in the chronic forms of these morbid appetites. 

 [Analogous to the pica of chlorosis and other anaemias in man, 

 and the dirt-eating habit of the an?emic hosts of uncinaria ; 

 probably many cases in animals are really expressions of a simi- 

 lar parasitism.] In rabid dogs there is a strong tendency to 

 swallow foreign bodies. In sows the habit of eating the pigs and 

 in ruminants of devouring the placenta are expressions of psychic 

 abnormalities. 



(For fuller details see Friedberger-Frohner, Veterinary Patliology, 

 Amer. Ed., 1904. W. T. Keener & Co., Chicago.) 



Motor Disturbances. — Aluscular movements are normally — 

 I, Voluntary, stimulated by the psycho-motor elements of the 

 gray cortical substance of the brain; 2. automatic, caused by chem- 

 ical stimuli, independently of voluntary influence, occurring 

 rhythmically and at all times present; 3. reflex, performed 

 unconsciously and caused by transmission of sensory excitation 

 to the motor apparatus; 4, co-ordinated and combined, the rapid 

 succession and repetition of voluntary and involuntary move- 

 ments as group actions, represented by facility of movement 

 acquired from practice (Samuel). Disturbances of movement 

 (motility) depend either upon pathological changes f'n the mus- 

 cles, tendons, bones and joints, or upon changes in the motor 

 nerves. The motor tract begins in the large ganglionic cells of 

 the central convolutions, passes by the long pyramidal fibres to 

 the cells of the anterior horns of the spinal cord and thence pass 

 peripherally by the nerves distributed to the muscles. In addition 

 those fibres and cells of the cerebral cortex which are concerned in 

 perception, ideation and volitional stimulation are more or less in- 

 volved in the production of voluntary movements. The complicated 

 and widely distributed tract may be exposed at any point in its 

 entire length to influences which are capable of interfering with 

 its functions. Such disturbances manifest themselves either as 

 pathological exaggeration or pathological impairment of motility. 



Pathological exaggeration of motility is manifested by spasms; 

 spasm or hyperkincsis (17 Kii>r)<ns) may be defined as a paroxysmal 

 muscular contraction which is occasioned by pathological stimu- 

 lation or which, if caused by ordinary stimuli, exceeds normal 



