SPECIAL ACTIONS ON HORSES 33 



system is better developed than their brain, are so sus- 

 ceptible to strychnine, which acts specially on the cord. 

 The human cerebrum, the seat of intelligence, is more than 

 seven times the weight of the mesencephalon and cerebellum. 

 In the domestic animals the cerebrum is only five times the 

 weight of the posterior parts of the brain, whilst the cord 

 is relatively larger than in man. These differences of de- 

 velopment explain how such medicines as opium, chloro- 

 form, and chloral cause in man blunted intellectual function 

 and deep stupor, while in the lower animals, with less marked 

 depression of brain function, they conjoin more marked 

 deranged motor function and convulsions. 



The Horse has a small stomach, and capacious, highly- 

 vascular intestines, adapted for absorption of nutriment 

 from bulky vegetable food. Nearly two- thirds of the water 

 in the ingesta pass off by the bowels, while in man only five 

 per cent, is removed by this channel, and the amount is 

 still less in dogs and cats. Vegetable purgatives, notably 

 aloes, appear more suitable than mineral purgatives. 

 Except in very rare diseased states, attempts at vomition 

 are not easily excited in horses. Tartar emetic, of which 

 a few grains cause immediate emesis in dogs, has no such 

 physiological effect on either horses or cattle. According 

 to some authorities, this insusceptibility of the horse to the 

 action of emetics is ascribable to an inaptitude of the vagus 

 nerve to receive and convey the special irritation, but more 

 probably it is due to imperfect development of the vomit- 

 ing centre. Actual vomition in horses is hindered by the 

 small stomach not being readily compressed between the 

 diaphragm and abdominal muscles, and by the stout band 

 of muscular fibres which surrounds its cesophageal opening. 

 The many sedatives available in human and canine practice 

 operate uncertainly and imperfectly on horses. The kidneys 

 of horses are easily stimulated ; in ordinary circumstances 

 they remove about one-seventh of the fluid ingesta, while 

 the same organs in man drain away 54 per cent., and in 

 dogs nearly 50 per cent, of the fluid discharges. Sudorifics 

 are less prompt than in man, and are apt to act on the kid- 

 neys, unless the animal be well clothed. 



In Cattle the peculiarities of the action of medicines are 



c 



