DISEASES OF CATTLE 385 



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 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 ex- 

 creted. 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 cer- 

 tainty when introduced beneath the skin, may be taken into the 

 stomach without causing inconvenience, as curara, the arrow poison, 

 or the venomous secretion 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 compound and becomes innocuous. Idio- 

 syncrasies are not so noticeable 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 herd of animals equally exposed injurious 

 or fatal effects do not appear with uniformity. For example, among 

 cattle that are compelled to drink water holding in solution a salt 

 of lead the effects of the poisoning will be found varying all the way 

 from fatality to imperceptibility. 



GENERAL SYMPTOMS OF POISONING. 



It is not always easy to differentiate between poisoning and some 

 disease. Indeed, examination during the life of the animal is some- 

 times wholly inadequate to the formation of an opinion as to whether 

 the case is one of poisoning or, if it is, as to what the poison may be. 

 A chemical and physical examination after the death of the animal 

 may be necessary to clear up the doubt. On the other hand, the 

 symptoms may be of such a nature as to point unmistakably to 

 poisoning with a certain agent. In general, the following classes of 

 symptoms may be regarded as indicative of poisoning: Sudden 

 onset of the disease without visible cause, a number of animals sim- 

 ilarly affected at once, severe gastro-intestinal disorder or derange- 

 ment of the nervous system, or both. Sudden alteration of heart 

 action in relation to frequency, force, or rhythm. Local irritation, 

 dyspnoea, or change in the urine or urination. 



After death lesions of the greatest variety may be found, and 

 it is necessary for one to be skilled in anatomy and pathology to 

 determine their significance. Oftentimes the stomach and intestines 



