52 DISEASES OF CATTLE. 



THE ACTION OF POISONS. 



The action of poisons may be either local, and exerted directly on 

 the tissues with Avhich they come in contact, or remote, acting through 

 the circulation or the nervous system ; or both local and remote action 

 may be exerted by the same drug. Poisons Avhich act locally gener- 

 ally either destroy by corrosion the tissues with Avhich they come in 

 contact or by inhalation set up acute inflannnation. When any cor- 

 rosive agent is taken into the stomach in poisonous quantities, a group 

 of symptoms is developed which is common to all. The tissues Avith 

 which the agent comes in contact are destroyed, sloughing and acute 

 inflammation 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 suffi- 

 ciently corrosive nature to destroy the tissues, but sufficiently irritat- 

 ing 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 different, 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 invohed. 

 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 b}^ 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 wdth 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 poisons, or the venomous 

 secretion of snakes. Other agents in chemical combination may 

 tend to intensifj^, 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 

 compound and becomes innocuous. Idiosj'^ncrasies are not so notice- 

 able in cattle practice as in practice among human beings, but the 

 uncertainty with which some drugs exert their influence would lead 

 us to believe that well-marked differences in susceptibility exist. 

 Even in some cases a tolerance for poison is engendered, so that in a 



