INTEODUGTION 19 



question as regards animals assumes 'interest in view of the 

 fact that cases of poisoning by the local poisonous plants 

 do not often occur amongst animals bred in a particular 

 locality. But it is almost certain that is due to their 

 avoidance of the dangerous herb. When frpsh stock is put 

 on the land, the animals eat indiscriminately, and poisoning 

 occurs. 



CLASSIFICATION. 



The rational basis of classification is that of physiological 

 action, but unfortunately no satisfactory scheme is avail- 

 able. In many cases the action is complex ; thus there may 

 be local effects and general effects, as with ammonia and 

 aconitine. There may be much overlapping as regards the 

 centres acted upon, making it difficult to assign a particular 

 poison to a particular class. The course of poisoning by 

 a plant is always complex. In the majority of cases 

 poisonous plants owe their activity to alkaloids, which act 

 after absorption. At the same time on account of other 

 components (acrid juices, oils, and the like) they exercise 

 irritant effects. The effects of a large poisonous dose are 

 not necessarily similar to those exercised by moderate 

 therapeutic administrations. 



A useful, if broad, distinction may be made between — 

 (1) corrosives, (2) irritants, (3) non- irritant nervous poisons. 

 Corrosives owe their action to their concentration, and are 

 represented by the strong mineral acids and alkalis, phenols, 

 and very concentrated solutions of many salts. A poison 

 acting as a corrosive in a concentrated form may have an 

 entirely different action in a diluted condition. Actual de- 

 struction by water abstraction, by decomposition, and solu- 

 tion of fats and proteins in the living cell mark the effect 

 of a corrosive. 



Irritants so modify the cell as to disturb its normal course 

 of metabolism, ultimately causing inflammation. The 

 irritant effect is general, not being limited to special cells 

 of the organism, and poisons having a wide range of activity 



