432 



Xerz'oiis Disturbances. 



sach locations also, as in affections of the spinal cord. In the 

 brain, as indicated by the absence of pain during operative pro- 

 cedures, the sensibility to pain is very low, at least in the cortical 

 areas. Only hairs, hoof, and cartilage, provided the matrix be 

 not also involved, are entirely devoid of the sense of pain, be- 

 cause of the absence of nerves from these structures. 



The existence of pain is shown in animals partly by general 

 symptoms (restlessness, pawing, stamping, running about, roll- 

 ing over, groaning, sighing, gritting the teeth, whining and cry- 

 ing shrilly), partly by local symptoms which suggest and more 

 or less clearly indicate the location of the painful trouble 

 (scratching, hobbling, protective movements when touched, strik- 

 ing against the abdomen, looking around toward the posterior 

 part of the body, arching of the back, symptoms of colic). 



Itching, indicated by the tendency to scratch, is met in cuta- 

 neous aft'ections, in some intoxications and general disturbances : 

 it must be due to an irritation of the nerve endings (pressure 

 points, Krehl), but the mode of origin is unknown. 



The irritative symptoms, ''formication," "going to sleep" of 

 some part, which are caused by pressure upon nerve trunks 

 iparcrsthcsia), light and color phenomena from irritation in the 

 optic tract (pJiotopsia, chrotnopsia), abnormal temperature sen- 

 sations, cannot be determined in animals, as they are subjective 

 perceptions. 



Pathological di^niniition of sensation. Tn lesions which inter- 

 rupt the course of the nerves at any position or render function- 

 less the parts subjected to irritation, sensation is entirely lost 

 or diminished or its transmission slowed. Sensory palsy (anccs- 

 thesia) may be induced by traumatic destruction of continuity 

 (nerve section, crushing), by freezing, cauterizing the endings, 

 by local anaemia, oedema, degeneration or atrophy of the peripheral 

 nerves or brain and cord segments, as well as by the local and 

 general action of certain medicaments (anodynes and anaes- 

 thetics, as morphine, chloroform, ether, chloral hydrate). Paraly- 

 sis of sensation may be total, so that practically every kind of sen- 

 sation is lost : or it may be partial, as when the sense of pain is 

 abolished and the pressure sense or sensitiveness to electrical irri- 

 tation is retained, or where the special senses are destroyed but the 

 sense of pain is intact. 



The results of disturbed sensation depend upon the impor- 

 tance of the physiological functions abolished. Anaesthesias of 



