DRUGS ACTING ON THE DIGESTIVE ORGANS 21 



Hants are likewise comparatively insusceptible to emetics 

 because of the large size of their digestive apparatus, which 

 is not easily compressed between the parietes and diaphragm. 

 Therefore the vomiting centre remains probably in a state of 

 non-development in the horse and ruminant, by reason of 

 non-use. 



Cattle and horses do, however, occasionally vomit. Cat- 

 tle at sea frequently suffer from mal de mer^ and the writer 

 has observed actual vomition in them following the use of 

 tartar emetic. Horses may vomit when the stomach is 

 greatly distended with gas. 



Emetics may be classed as : 1. Specific^ acting on the 

 vomiting centre through the blood. 2. Locals by stimula- 

 tion of the sensory nerve-endings in the mouth, throat, gullet 

 and stomach. 3. Mixed^ those acting in both ways. 



It is impossible, in our present state of knowledge, to 

 apply this classification accurately to individual drugs, but 

 the following statements may be made : If an emetic is in- 

 jected into the blood and vomiting instantly occurs, the drug 

 has probably acted upon the vomiting centre ; if some time 

 elapses before the occurrence of vomition, it is probable that 

 the drug has acted upon the stomach during its elimination 

 by that organ. Contrariwise, if, after the ingestion of an 

 emetic, a considerable period intervenes before vomiting 

 comes on, it is probable that the agent has acted on the 

 vomiting centre. 



Again, if a larger quantity of a drug is required when 

 injected into the blood than when swallowed, to cause 

 emesis, it is fair to suppose that the agent acts on the 

 stomach directly or during its elimination. Finally, if an 

 emetic is thrown into the blood after the removal of the 

 stomach and substitution of a bladder in its place, and vom- 

 iting does not occur (Majendie's experiment with tartar 

 emetic), it shows that the agent only acts on the stomach ; 

 but if vomiting does occur, it indicates that the agent acts 

 on the vomiting centre and causes emesis by contraction of 

 the parietes and diaphragm, with this reservation, that the 



