Focal Symptoms. 591 



is preceded by convulsions owing to stimulation of the cells be- 

 fore they are destroyed. 



The further the disease is removed from the cortex the 

 smaller the diseased area sufficient to partially or completely de- 

 stroy the converging motor path. In the depth of the white 

 matter and still more in the internal capsule and the crura 

 cerebri somewhat more extensive lesions may cause paralysis 

 of the opposite side of the body (hemiplegia). In cases where 

 the crus, pons, or commencement of the medulla is injured it 

 usually happens that the central motor path and the nucleus or 

 basal process of some cranial nerve is involved, resulting in 

 nuclear or infranuclear paralysis of the cranial nerve on the 

 same side as well as partial or total paralysis of the other side 

 of the body. In cases where the the disease affects the nucleus 

 of origin of the nerve or the nerve root there is paralysis of the 

 part supplied by the cranial nerve alone. 



Unilateral paralysis due to disease of the central motor 

 path and involving muscles that work in concert on both sides of 

 the body (eyes, mastication, muscles of the trunk) generally 

 passes unnoticed, although the paralysis, as a rule, is incomplete 

 in muscles that operate on both sides of the body independently 

 and is, as a rule, most obvious in movements that are not auto- 

 matic. The course followed by the extrapyramidal tract makes 

 it possible that in addition to marked paresis of the opposite 

 side there may be a certain degree of weakness in the muscles 

 of the diseased side. Clinical observations and animal experi- 

 ments adduce further proof that paralysis due to lesions of the 

 central motor path not rarely disappear either completely or to 

 a great extent in time. 



The principal focal symptom is ataxia. 



Under the term ataxia are included all obvious functional disturbances of 

 muscles that are not due to loss of power and are not the result of paralysis. Prom 

 this it follows that ataxia is due to some interruption in the sensory portion of the 

 coordinating system, that is in the centripetal portion. Great care must be exercised 

 in the diagnosis of ataxia in order to avoid the inclusion of an actual paralysis under 

 the term. True ataxia is very rarely observed in animals. It far more frequently 

 happens that ataxia and paralysis are present at the same time and it is very 

 difficult to decide to what extent the abnormal movements are due to paralysis and 

 to what extent due to ataxia. 



It is customary to distinguish between peripheral, spinal, cerebellar, and cere- 

 bral ataxia, depending upon the seat of the lesion. When there is disease of the 

 peripheral sensory nerves all the nerve fibers passing to the spinal cord or medulla 

 and from thence to the cerebellum or cerebrum are blocked causing very severe 

 motor and static ataxia. It would be unusual if the motor fibers in a mixed nerve 

 were not also involved, in which case there would of necessity be paralysis also. In 

 view of the faot that the sensory tracts run in different columns in the spinal cord 

 it is quite likely that in cases of localized disease some of the other paths may re- 

 main intact. Owing to this, spinal ataxia may be less pronounced than peripheral, 

 and according to the localization of the disease may be obvious in connection witli 

 movement or equilibration. Eeferences to spinal ataxia in veterinary literature are 

 very frequent, but accurate knowledge shows that pure cases of the condition are 

 very rare and that in the majority of instances it is associated with spinal paralysis. 

 In cases of cerebral or cortical ataxia there is an absence of fine gradations of 

 movement, in carrying out any movement the muscles contract with greater force 

 than is necessary or the action may involve a greater or smaller number of muscles 

 than is necessary with the result that the movement is clumsy. Cerebellar ataxia, which 



