2i8 THE HUMAN SPECIES 



In addition to the motor-fibres the vagus contains sensory- 

 fibres which pass to the pharynx, oesophagus and stomach. 



Vomiting of the contents of the stomach takes place very 

 easily in carnivora and omnivora (man and apes), because the 

 cardiac orifice remains open while the pylorus is firmly closed. 

 Even in insectivora the act is easy, but it is less so in rodents 

 and ruminants, and rare in horses except when the cardiac orifice 

 is torn. If the vagus is divided in any animal, vomiting be- 

 comes either impossible or incomplete, because the musculature 

 of the pylorus and cardia are cut off from the necessary stimu- 

 lating source. 



The duration of gastric digestion is roughly the same in man 

 and the omnivora ; this holds good of intestinal digestion too. 

 In all mammals the amount of chyme absorbed by the 

 stomach is very small, the bulk of it being absorbed by the 

 intestine according to the laws of osmosis. The chyme after 

 leaving the stomach is further exposed to the action of the 

 bile, the pancreatic juice and the succus entericus, whereby its 

 reaction is gradually changed from acid to the neutral condi- 

 tion which favours absorption. 



The bile, which is formed in the liver, flows directly into 

 the duodenum without first accumulating in a gall-bladder in 

 Ungulates and Cetaceans, in certain Ruminants (the deer, camel 

 and dromedary), in certain Pachyderms (the elephant and rhino- 

 ceros), and in certain Rodents (the beaver, marmot and rat). 

 All other mammals and birds are provided, like man, with a 

 gall-bladder. 



Human bile is of a yellowish-brown colour inclining to 

 green, similar to that of most animals. It has a characteristic 

 musk-like odour, and a higher specific gravity in man than in 

 any other animal, for while in other animals it ranges up to 

 1005, in man it is between 1026 and 1032. The quantity 

 secreted daily is the greater in proportion to the body-weight 

 the smaller the animal (especially herbivora). As a rule, the 

 secretion is relatively greater in herbivora than in carnivora and 

 omnivora ; the following table gives the amount secreted by a 

 biliary fistula in twenty-four hours per kilogramme of body- 

 weight : l 



1 Munk-Schultz, loc. cit., p. 167. 



