186 BOVINE PATHOLOGY. 



medicines. Thus, we may revert to our table of medi- 

 cinal agents as classified, and shall be able to examine 

 poisons under the various headings there indicated. Of 

 Hsematics, acids, alkalies, tonics, and chaljbeates do not 

 exert a toxic action by passing into the blood, but by 

 their irritant and astringent effects upon the surfaces 

 with which they come into contact. Hence they must be 

 considered somewhat as astringents and arranged with 

 astringents in the Irritant division. Again, general 

 stimulants cannot be considered poisonous in the same 

 sense of the term, for they simply accelerate vital process. 

 It is only the most powerful of them which exert any direct 

 toxic effects, as oxygen gas when inhaled in an undiluted 

 condition. Thus we classify poisons as — 



["Special stimulants, as strychnia. 

 Neueotics J Narcotics, as belladonna. 



I Sedatives I ^^"^.^f' ^s prussic acid. 



{_ I Special, as digitalis. 



r Simple irritants, as mustard. 

 J J Corrosives, as bichloride of mercury. 



1EEITANTS< Astringents, as oak shoots. 



[_Eliminatives, as nitrate of potash. 



With regard to the particular conditions of the animal to 

 which poisonous agents are administered, we must remem- 

 ber the phenomena of idiosyncrasy and toleration. Large 

 quantities of most vegetable agents are necessary to exert 

 a poisonous action on herbivora, and a small amount of 

 animal poison is effectual, but there are marked exceptions 

 to this as to all other rules. The phenomenon of tolerance 

 is the condition of becoming accustomed to the remedy, so 

 that larger doses are required than at first to produce medi- 

 cinal effects. Sometimes, however, agents are cumulative, 

 so that successive doses at length simultaneously exert their 

 action and may thus destroy the patient. This results in 

 the case of those agents which are not readily thrown off 

 from the system by the excretory organs. We see this 

 in the action of digitalis, which only after several doses is 

 removed by the kidneys. Certain diseases may be con- 

 founded with poisoning, and it is a matter of extreme 

 difficulty in some cases to make a correct diagnosis. We 

 shall not be surprised at this if we consider that poisons 



