388 ARSENIC, ANTIMONY AND PHOSPHORUS 



several times the toxic ones. Sometimes animals become immune 

 from long continued dosing and " arsenic eaters " are very tolerant to 

 it. This acquired immunity from doses by the digestive tract is prob- 

 ably due to an acquired resistance to absorption, because such ani- 

 mals are no more resistant to its administration subcutaneously than 

 others not previously treated. 



Toxicology. Arsenic poisoning is one of the most common 

 found in veterinary practice. It may be caused by the injudicious 

 use of the drug by the laity, may be administered v^ith intent to 

 kill, may be due to careless use of arsenical mange dips, where ani- 

 mals are allowed to drain on the forage, to pasturing in orchards in 

 which the trees have been sprayed with arsenical preparations, or to 

 pasturing on land in the region of smelters, in which case the ar- 

 senic is deposited on the forage and is taken in by the animals; or 

 it may be due to carelessness with arsenical preparations used as 

 insecticides, or in rat poisons. 



According to Law, the toxic dose for the horse is 140 grains in 

 solution or 3/4 drams in powder, cattle 3% drams to T drams, sheep, 

 2 drams, dogs, 2 grains, but they may recover from larger doses 

 because the larger amounts cause emesis. Hogs may die after re- 

 ceiving 15 grains, but, as in case of dogs, may recover from larger 

 ones. 



Poisoning from arsenic may be either acute or chronic. 



Acute Poisoning. The symptoms of acute arsenic poisoning 

 are violent colic, weak, irregular, rapid respirations, emesis in vomit- 

 ing animals, great thirst, violent purging, cold extremities, nervous 

 disturbances consisting of stupor, trembling, convulsions or paraly- 

 sis. Acute poisoning points to a very rapid absorption because it 

 sets in early. The first noticed symptom is violent gastroenteritis 

 which so closely resembles that of corrosive poisoning that it was 

 formerly believed to be due to the corrosive action of arsenic. The 

 action of arsenic, however, is not strictly local because subcutaneous 

 doses or intravenous doses will produce the same lesions in the 

 gastrointestinal tract as when administered by mouth. Turther- 

 more, arsenic preparations do not form compounds with the pro- 

 teids, analogous to those of the heavy metals and require a certain 

 period before their action is seen, while corrosives produce their 

 effects at once. On account of the above facts, it is generally believed 

 that the action of arsenic is due largely to its effects after absorp- 

 tion. 



Blood pressure falls at the beginning of symptoms of poisoning, 

 due probably to a dilatation of the blood vessels. This is shovm by 

 the fact that if the aorta is cl^imped, the heart will keep up a good 

 pressure. The paralysis is believed to be in the capillaries, because 

 the arterioles will still contract if the peripheral stump of the splanch- 



