340 COMPARATIVE PHYSIOLOGY. 



protect the nasal passages, The stomach and cesophagus are 

 not wholly passive, though the part they take actively in vom- 

 iting is variable in different animals. 



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 

 oiu" dogs and cats ; a matter of importance to an animal accus- 

 tomed 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 stomach of the human being during infantile life is less 

 pouched than in the adult, which in part explains the ease with 

 which very young children vomit. 



It is well known that the horse vomits rarely and with great 

 difficulty. This has been attributed by different writers to va- 

 rious conditions of a structural kind, such as the length of the 

 gullet ; the manner in which it enters the stomach (centrally) ; 

 the pressure of a tightly closing sphincter at this point ; the 

 valve-like foldings of the mucous membrane at the cardiac 

 opening ; the small size of the stomach and its sheltered posi- 

 tion, so that the abdominal muscles can not readily act on it ; 

 the existence of a considerable length of the oesophagus be- 

 tween the stomach and diaphragm which is against dilatation 

 of the orifice by the longitudinal fibers of the gullet ; the open 

 pylorus, permitting of the gastric contents being driven into the 

 intestines rather than upward. 



But in the ox these peculiarities do not exist; in fact, from a 

 mechanical point of view, the structure and relation of parts is 

 favorable, yet this animal seldom vomits, and never with ease. 

 Why does the horse vomit after rupture of the stomach when 

 conditions are less favorable from a mechanical point of view ? 

 There is the greatest difference as to the readiness with which 

 different human beings vomit ; moreover, persons that vomit 

 usually with difficulty may do so very perfectly when suffi- 

 ciently prepared, as by sea-sickness. 



These and many other considerations have led us to conclude 



