INTERNAL DISEASES 413 



horses and dogs is due, as in man, to acute or chronic patho- 

 logical changes in the spinal cord above the paralysed part. 

 Schmidt has noted such total, or partial, paralysis in apes, 

 canines, and other beasts of prey in zoological gardens. 



Paralysis of certain sensory nerves in the lower extremity is 

 very rare, and only seen in horses and large dogs. The nerves 

 most frequently involved are those supplying the thigh and 

 shin and calf. Still less frequent is paralysis of the two mixed 

 nerves the crural and obturator. 



Pathological irritation of sensory nerves (neuralgia) is 

 probably similar in animals and man, but is difficult to diag- 

 nose. Pathological irritation of motor nerves (spasm) is most 

 clearly seen in the so-called springhalt in horses : it is probably 

 due to a painful sciatica, and consists of regularly recurring 

 spasms of the posterior thigh muscles. Schmidt notes that 

 muscular spasms accompany certain diseases in apes, and are 

 still more frequent symptoms in beasts of prey. 



The neuroses seen in men, which manifest themselves in 

 motor disturbances of various kinds, are also reproduced in certain 

 animals. Horses, and according to Schmidt apes and jackals, 

 suffer from epilepsy. Eclampsia is commonest in young dogs 

 and pigs, less frequent in bitches and other grown animals, such 

 as cows ; catalepsy is very seldom seen (prairie wolf, wolf, dogs, 

 horses, cattle). St. Vitus' dance is also observed in young dogs 

 and jackals. Two severe diseases depending on pathological 

 changes in the thyroid gland, especially as regards the suppres- 

 sion or increase of its internal secretion, show the close relation- 

 ship of human to comparative pathology. Cretinism and 

 myxcedema, which depend upon degeneration of the thyroid 

 gland and suppression of its internal secretion, are unknown in 

 aninjals, either in the endemic or sporadic form. Records of 

 well-established cases are available, in which, after complete 

 extirpation of the thyroid, owing to goitre, cachexia strumpriva, 

 similar exactly to that seen in man, was observed. The re- 

 verse of hypothyroidism is hyperthyroidism, which in man 

 gives rise to Graves' disease (proptosis, goitre and severe nervous 

 disturbance of the heart) ; it is not infrequently seen in certain 

 animals (dogs, horses, cattle). 



Mental Diseases. Can animals become mentally deranged ? 



