18 VETEEINAEY TOXICOLOGY 



accounts partially for the usually high degree of resistance 

 of the ox and goat. 



The relative stage of development of the nervous system 

 greatly afifects the dosage and action of many drugs. , In 

 illustration, the dog is more susceptible to morphine than 

 the rabbit and less so than man. Morphine acts as an 

 hypnotic on man and the dog, but as an excitant and 

 convulsive on the cat, goat, pig, ox, and horse. 



But some variations cannot easily be explained on such 

 considerations. Thus, the ox is considerably more sensitive 

 to mercury and lead than the horse ; the rabbit is insensi- 

 tive to atropine ; birds withstand large doses of strychnine. 



VARIATIONS OF ACTION DUE TO THE INDIVIDUAL. 



Ag"e.- — As a rule, young animals are more sensitive than 

 adults, but the young cat is less susceptible to morphine 

 than the old, and young animals are less affected by 

 strychnine than older ones. On the other hand, according 

 to Frohner, whilst a dog of ten years can resist 1"7 grams 

 of santonine per kilogramme, 0*2 grammes per kilogramme 

 will kill a dog of a few weeks old. 



Idiosyncracy. — Subjects apparently similar in all respects 

 often display great diversity in relation to a drug. Thus, 

 strychnine sometimes is dangerous in ordinary medicinal 

 doses to dogs, on account of which, as also by reason of the 

 accumulation due to tardy elimination, dosage of this drug 

 ought to be kept down. 



In poisoning, where a large overdose is almost always 

 given, there is not so much room for the display of 

 idiosyncracy as in therapeutic treatment. 



Other factors of tolerance and habituation do not play a 

 significant part in toxicology on the same grounds of the 

 large dose commonly given. Habituation is displayed 

 towards nervous poisons in man — e.g., opium, nicotine, 

 alcohol, and probably also towards arsenic, of which the 

 mountaineers of Styria eat relatively large quantities. The 



