FORMS OF MENTAL DEFECT AND DERANGEMENT. 47 



nically known in its highest degree as senile dementia. In 

 age, in the lower animals as in man, mental decay or de- 

 generation accompanies pari passu physical disability. Loss 

 of memory, of will, of intelligence, accompany loss of mus- 

 cular vigour, and a vegetative life results. But this senile 

 imbecility or dementia is seldom seen except in domestic pets, 

 such as dogs, cats, horses or ponies, and parrots, which are 

 occasionally allowed to die a natural death. 



It is important to note here that the pathological bases 

 of senile dementia in the dog and in man are alike. Not 

 only are the symptoms the same in kind, but the struc- 

 tural cerebral lesions, on which they depend, or with which 

 at all events they are associated, also present a remarkable 

 similarity in the two classes of cases. Thus Dr. Major tells 

 us that the symptoms in the dog ' present in some respects a 

 remarkable similarity with those of the analogous condition 

 in man,' being in both cases referable to a condition of 

 atrophy of the 'cerebral hemispheres and degeneration of 

 those nerve-elements which form their most important con- 

 stituents.' * I have no doubt that when other forms of 

 mental defect or derangement in the lower animals are 

 compared in an equally careful way with the corresponding 

 conditions in man, not only the symptoms but the patho- 

 logical lesions and conditions will be found in other cases 

 equally wonderfully alike. 



Dementia, however, in its different degrees between slight 

 weakness or want of intelligence, and absolute non- 

 intelligence or fatuity, is not confined to the periods of youth 

 or age. It is liable to occur at all stages of life, sometimes 

 in an acute, rapidly-developed form, but more usually it is 

 gradually developed as the termination of, or sequel to, other 

 more acute forms of insanity, especially mania and melan- 

 cholia. Pierquin describes dementia 



1. In the horse, from passion, blows on the head, disease 

 of the brain or its membranes ; 



2. In the mule, from acute encephalitis; and 



3. In the cat from fright. 



Arboval too speaks of it as following passion, bad usage, blows 



1 Wakefield Reports,' vol. v. p. 161. 



