54 DISEASES OE CATTLE. 



insects, may have become poisonous, producing forage poisoning, meat 

 poisoning, cheese poisoning, etc. 



(4) Poisonous plants in the pasture or forage. 



(5) The bite or sting of a poisonous insect or the bite of an animal. 



(6) Malicious poisoning. 



THE ACTION OF POISONS. 



This may be either local, and exerted directly on the tissues with 

 which they come in contact, or remote, acting through the circula- 

 tion or the nervous system ; or both local and remote action may be 

 exerted by the same drug. Poisons which act locally generally either 

 destroy by corrosion the tissues with which they come in contact or 

 by inhalation set up acute inflammation. When any corrosive agent 

 is taken into the stomach in poisonous quantities, a group of symp- 

 toms is developed which is common to all. The tissues with which 

 the agent comes in contact are destroyed, sloughing and acute inflam- 

 mation of the surrounding structures take place; intense pain in the 

 abdomen and death ensue. In a like manner, but with less rapidity, 

 the same result is reached if the agent used be not of a sufficiently 

 corrosive nature to destroy the tissues, but sufficiently irritating to set 

 up acute inflammation of the mucous membrane of the digestive tract. 

 If the poison exerts a remote influence alone, the action is quite differ- 

 ent, little or no local effect being produced upon the digestive organs. 



To produce an effect on some part of the body distant from the 

 channel of entrance, a poison must have been absorbed and carried 

 in the blood to the central nervous system or other region involved. 

 The poisonous effect of any substance is modified by the quantity 

 used ; by its chemical combinations ; by the part of the animal struc- 

 ture with which it comes in contact; by the physical condition of the 

 subject; and also by the rapidity with which the poison is excreted. 

 As an illustration, opium may be given with safety in much larger 

 doses to an animal suffering from acute pain than to one free from 

 pain, and to an adult animal with greater safety than to a young one. 

 The rapidity with which the poison is absorbed, owing to the part of 

 the body with which it is brought in contact, is also an important 

 factor. So marked is this quality that some agents which have the 

 power of destroying life with almost absolute certainty when intro- 

 duced beneath the skin, may be taken into the stomach without caus- 

 ing inconvenience, as curara, the arrow poison, or the venomous secre- 

 tion of the snake. Other agents in chemical combination may tend 

 to intensify, lessen, or wholly neutralize the poisonous effect. For 

 example, arsenic in itself has well-marked poisonous properties, but 

 when brought in contact with dialyzed iron it forms an insoluble com- 

 pound and becomes innocuous. Idiosyncrasies are not so noticeable 

 in cattle practice as in practice among human beings, but the uncer- 

 tainty with which some drugs exert their influence would lead us to 



