HORSES AND RUMINANTS DO NOT VOMIT 105 



retching and discharge of excessive secretion of saliva rather 

 than true vomiting. The insusceptibility of horses to the 

 action of emetics is due apparently to some undiscovered 

 peculiarity of the nervous mechanism concerned in vomition 

 in most other animals. The horse's inability to regurgitate 

 matters from the stomach, even when attempts to vomit are 

 excited, depends upon several conditions on the smallness 

 of the stomach, which prevents it, even when tolerably full, 

 from being grasped and squeezed between the abdominal 

 muscles and the diaphragm ; on the strong horse-shoe-like 

 band of fibres which guards the cardiac orifice ; and on the 

 greater length of that portion of the oesophagus between the 

 diaphragm and stomach, which bends on itself, and thus 

 more securely obstructs the cardiac orifice when the tube, 

 under the influence of emetics, is shortened by the contrac- 

 tion of its longitudinal fibres. The contents of the horse's 

 stomach, even if discharged upwards, owing to the position 

 and length of the soft palate, would pass out by the nostrils, 

 and not by the mouth. As cattle naturally ruminate, it 

 might be supposed that they might also readily perform the 

 analogous act of vomiting ; but the substances which cause 

 emesis in other animals have no such effect on cattle or sheep. 

 This, in part, depends upon the large size of the subdivided 

 stomach, which cannot be grasped and compressed between 

 the' abdominal walls and diaphragm. In horses and rumi- 

 nants, the arrangement of the digestive organs thus virtually 

 preventing vomiting, the vomiting centre would not be 

 required ; if it ever existed amongst earlier races, it has 

 become dwarfed or ineffective, as seems evident from the 

 notable tolerance which horses have of tartar emetic. Sir 

 John M'Fadyean suggests that in ruminants the power to 

 vomit has perhaps been merged into the habit of rumination. 

 Emetics are divisible into two classes : 



(1) Those which mainly act locally on the stomach, such 



as copious draughts of tepid water, ipecacuanha, 

 solutions of salt, mustard, alum, and ammonium 

 carbonate, with copper and zinc sulphates. 



(2) Those which act, through the circulation, on the 



vomiting centre, such as apomorphine. Muscarine, 

 digitalis, pilocarpine, and the saponins, such as 



