DRUGS ACTING ON THE DIGESTIVE ORGANS 21 



of the abdominal walls and the diaphragm. In this process the stomach 

 is squeezed between the abdominal walls and diaphragm, and contraction 

 of the longitudinal fibres, radiating from the lower end of the gullet, 

 draws the stomach towards the diaphragm and so pulls open the cardiac 

 orifice, while the pylorus is firmly contracted and closed. Some pecu- 

 liarities may be noted in reference to vomition in the domestic animals. 

 Dogs, pigs and cats vomit readily and may be placed in the same category 

 as man in this respect. Horses rarely vomit and are not easily nauseated 

 by emetics. Vomiting is prevented in these animals by: 1. The small 

 size of the stomach, which is not readily compressed between the abdomi- 

 nal walls and diaphragm. 2. The length of the gullet between the 

 stomach and diaphragm, which form a valve-like obstruction when the 

 tube is shortened by contraction of the longitudinal fibres at its lower 

 extremity in attempts at vomition. 3. A horseshoe-like band of fibres 

 at the cardiac orifice, which hinders dilatation of this opening. Rumi- 

 nants 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 rumi- 

 nalit, by reason of non-use. 



Cattle and horses do, however, occasionally vomit. Cattle at sea fre- 

 quently suffer from mal de mer, and the writer has observed actual vomi- 

 tion in them following the use of tartar emetic. Horses may vomit when 

 the stomach is greatly distended with gas. 



Emetics may be classified as: 1. Specific, acting on the vomiting 

 centre through the blood. 2. Local, by stimulation 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 state- 

 ments may be made: If an emetic is injected into the carotid and vom- 

 iting instantly occurs, the drug has probably acted upon the vomiting 

 centre ; if some time elapses before the occurrence of vomition, it is prob- 

 able that the drug has acted upon the stomach during its elimination by 

 that organ. Contrariwise, if, after the ingestion of an emetic, a consider- 

 able 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 vomiting 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 drug may 

 have been eliminated by the esophagus and intestines and have reflexly 

 stimulated the vomiting centre through the medium of these parts. These 

 remarks demonstrate the complexity of the subject. 



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