DIGESTION OF FOOD. 339 ~ 
As the expulsive effort takes place, it is accompanied by an 
expiratory act which tends to keep the egesta out of the larynx 
and carry them onward, though it may also contribute to over- 
come the resistance of the elevated soft palate, which serves to 
protect the nasal passages. The stomach and cesophagus are 
not wholly passive, though their part is not so important in 
the adult as might be inferred from observing vomiting in 
infants, the peristalsis of these organs apparently sufficing in 
them to empty the stomach. 
Retching may be very violent and yet ineffectual when the 
cardiac sphincter is not fully relaxed. The pyloric outlet is 
usually closed, though in severe and long-continued vomiting 
bile is often ejected, which must have reached the stomach 
through the pylorus. 
Comparative.—The ease with which some animals vomit in 
comparison with others is extraordinary, as in carnivora like 
our dogs and cats; a matter of importance to an animal ac- 
customed in the wild state to eat entire carcasses of animals— 
hair, bones, etc., included. 
The readiness with which an animal vomits depends in great 
part on the conformation and relations of the parts of its digest- 
ive tract. 
The horse vomits with difficulty—its stomach and its car- 
diac opening being small and peculiar in shape (Figs. 261 and 
280), while its esophagus is long. The stomach of the human 
being during infantile life is less pouched than in the adult, 
which in part explains the ease with which infants vomit. 
But the matter is complex; much depends on the proper 
co-ordinations being made, and, this being well or ill accom- 
plished, accounts for the variations in the ease with which dif- 
ferent persons vomit. 
Pathological —Vomiting may arise from the presence of renal 
or biliary calculi (reflex action); from disease of the cerebrum 
or the medulla; from obstruction in the pyloric region or in 
the intestines; from emotions; from revived unpleasant men- 
tal associations; from nauseous tastes, etc. It may be ques- 
tionable whether some of these are properly termed “ patho- 
logical.” 
Pyrosis is due to the anti-peristaltic action of the stomach 
and csophagus alone, so that it is a sort of partial vomiting 
and allied to the regurgitation of special secretions, as from the 
crops of pigeons, or of food from the stomachs of ruminants. 
We have known cases in which anti-peristalsis was confined to 
