NERVOUS SYSTEM. 21.} 



Decreased sensibility is called hypesthesia, absence of 

 sensibility is called anesthesia, abnormally increased sensibil- 

 ity is called hyperesthesia. Sometimes sensibility is retarded; 

 this is indicated when the reaction occurs an unusually long 

 time after the stimulus is applied. 



Hyperesthesia is most frequently seen in old 

 ticklish mares, also in lumbar prurigo of sheep and in 

 the first stages of cerebritis. 



Diminished sensibility is observed in chronic affections of 

 the brain, immobility, tumors, second stage of acute cerebritis, 

 parturient fever, second stage of cerebro-spinal meningitis, and 

 in narcotic poisonings. 



III. Motility. 



In morbid conditions affecting the cerebral hemispheres 

 only we observe no serious disturbances in motility because the 

 mid brain and the cerebellum are the seat of co-ordinated 

 movements. 



a. Spasms, or cramps, are involuntary muscular con- 

 tractions. Spasms of short duration, alternating with relaxa- 

 tions, are called clonic spasms ; if they are very slight, uni- 

 form, rapid, and locally limited we call it trembling; if they 

 affect large areas or extend over the whole body we call them 

 convulsions. Clonic spasms are observed in partial and gen- 

 eral epilepsy and in inflammatory affections of the brain and 

 spinal cord (common after dog distemper). Tonic or tetanic 

 spasms are muscular contractions that continue for some time 

 without relaxation. They are characteristic for tetanus (lock- 

 jaw) and strychnine poisoning, causing the body to assume 

 a stiff position, especially the head, neck, ears, back, and tail. 

 The mouth is closed as a result of contraction of masseter 

 muscles, nostrils distended "trumpet like." Stiffness of the 

 back without bending is called orthotonus, depression of 

 spinal column and bending back of head toward withers, opis- 

 thotonus, spasms of the masseter muscles, trismus, spasms of 



