280 PHYSIOLOGY. 



contraction of the muscles of the pharynx, and then by a 

 successive contraction of the circular fibres of the gullet it- 

 self, from above downwards. That the morsel is not carried 

 down merely by its own weight, is proved by the fact, that 

 a man can swallow with his head downwards. 



15. In the stomach, the food is converted into a soft, grey, 

 pulpy mass, called chyme. This process has been called 

 chymosis. It is produced by the motions of the stomach, 

 together with the agency of the secretions, which are thrown 

 out by the gastric vessels. These motions have been called 

 vermicular or worm-like ; and undulatory, or like wave suc- 

 ceeding wave. The crawling of a worm furnishes a very 

 good illustration of the successive contractions of the muscu- 

 lar fibres of the stomach, commencing, as they do, at the aeso- 

 phagus, and proceeding onwards to the pylorus, and so back 

 again. These motions of course bring every portion of the 

 contents of the stomach in contact with all parts of its sur- 

 face ; and so they become intimately mixed with the gastric 

 fluid. 



16. The food is thus carried round the interior of the sto- 

 mach, from one extremity to the other ; and from one to 

 three minutes are employed in each revolution. In the mean 

 time, both orifices are closed ; so that the contents cannot 

 escape. During this process, the gastric fluid is secreted in 

 large quantities, and becomes mixed with the food as it 

 passes round. In a short time, the taste, smell, and other 

 sensible properties of the food, are entirely changed. This 

 is produced by the agency of the gastric juice, which sub- 

 verts the chemical affinities of the food ; and with its ele- 

 ments forms new combinations. 



17. fThe gastric fluid is a clear, transparent fluid, produced 

 by arterial exhalation ; acid to the taste, slightly saline, and 

 free from odour.] It possesses the singular property of co- 

 agulating albumen ; resists the putrefaction of animal mat- 

 ter ; and dissolves nearly every kind of alimentary substance. 

 Its acid properties are owing to the muriatic and acetic acids 



