64 DISEASES OF CATTLE. 



their baneful influence, and though some of them act with extreme 

 rapidity no effect can be produced until the agent has been absorbed. 

 The poisonous effect of any substance is modified by the quantity used ; 

 by its chemical combinations; by the part of the animal structure with 

 which it conies in contact; and also by the physical condition of the sub- 

 ject. 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 introduced beneath 

 the skin, may be taken into the stomach without causing even notice- 

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

 tion of the snake fang. 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. Idiosyncracies 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 vary- 

 ing all the way from fatality to iinperceptibility. 



GENERAL, SYMPTOMS OF POISONING. 



So widely varied are the symptoms produced by different poisonous 

 agents that it is almost impossible to lay down even a general rule of 

 symptoms which may be applied to all cases. Ordinarily, poisoning is 

 not suspected until after the death of the affected animal. To estab- 

 lish the presence or absence of poison in the system becomes necessary 

 only with a view to arresting its effect on other animals that may have 

 been similarly exposed, or to promote the ends of justice in criminal 

 jurisprudence. The symptoms shown before death are likely to give 

 reason to suspect either intestinal irritation, with manifestation similar 

 to those of colic ; or disordered brain function with the characteristic 

 indications of vertigo, coma, paralysis, dilatation, or contraction of the 

 pupil, etc. The animal secretions and excretions may be perverted, 

 augmented, or suppressed. Chemical analysis and philosophical expe- 

 riments only can determine with absolute certainty the presence of 

 many of the poisons. On the other hand, diagnosis may be reached 

 with reasonable certainty where the previous history of the case is 

 known, as well as the surroundings and the poisonous agents to which 

 the animal would be likely to have access. 



