474 OPIUM EFFECTS ON HORSES, CATTLE, DOGS 



dog little change is seen, but the action is a central one and 

 the pupil is not affected by topical applications. 



Different animals are somewhat differently affected by 

 opiates, depending upon the relative development of differ- 

 ent parts of their central nervous system. The higher the 

 development, the greater is the susceptibility of an organ to 

 the operation of the drugs which act upon it. Compared 

 with the lower animals, the cerebrum of man is relatively 

 heavier and more highly organised than the mesencephalon, 

 the cerebellum, and the spinal cord ; and this explains why 

 opiates given to man in relatively small doses quickly and 

 without marked stimulation paralyse the human cerebral 

 centres, inducing sleep, and, in large doses, coma. Horses, 

 with less development of these higher brain centres, have 

 relatively more development of the locomotor centres and of 

 the reflex centres of the spinal cord, and upon these lower 

 centres opiates in equine subjects exert their primary 

 stimulant effects. Full doses produce, at first, restless, 

 involuntary movements of the head and limbs, pawing, or 

 walking continuously round the box ; followed by sleepi- 

 ness, disinclination to move, and when moved staggering. 

 Excessive doses cause tetanic convulsions. 



Ruminants, like horses, are usually excited and restless. 

 Cattle bellow, digestion is deranged, and tympanites fre- 

 quently supervenes. Sleep is not quickly or readily induced, 

 excepting by full and repeated doses. 



Dogs exhibit effects intermediate between those observed 

 in man and in horses. Relatively to their body- weight, they 

 take eight or ten times the doses prescribed for man. They 

 show more preliminary excitement than man, but less 

 involuntary muscular movement than the horse, and during 

 drowsiness and sleep muscular twitchings occur. Sleep, how- 

 ever, is never very profound ; the dogs are easily awakened ; 

 they dream, and appear to have hallucinations, and after 

 full doses remain stupid for a day. There is some salivation, 

 in the majority of cases vomiting occurs, and often defseca- 

 tion. After twenty minutes or so the narcosis is sufficiently 

 pronounced to permit of even major operations, such as 

 amputations and laparotomy. Although the skin is con- 

 gested and hot, there is no notable increase of secretion 



