166 PHYSIOLOGY CHAP. 



By this method the following conclusions were arrived at : 



The mechanism of deglutition varies according to the animal 

 and the nature of the food swallowed. 



In fowls, the movement is slow and peristaltic whatever the 

 consistence of the food. Any jerking of fluid is obviously 

 impossible, because the parts surrounding the buccal cavity are 

 too hard and rigid. Gravity has a predominating importance 

 over the propulsive power of the mouth. Each time the mouth is 

 filled with fluid the head is raised, so that the liquid descends by 

 its own weight into the oesophagus, where it is carried forward by 

 peristalsis. 



In cats, according to these authors, the movement of deglutition 

 is always peristaltic and much more rapid than in fowls. The 

 bolus takes 9-12 seconds to reach the stomach. In the upper part 

 of the oesophagus, fluids move more rapidly than semi-solids. In 

 the lower or diaphragmatic parts the velocity, for both liquids and 

 solids, is much less than in the upper parts. 



In dogs, the bolus descends to the stomach in 4-5 seconds. 

 It is always propelled rapidly in the upper part, and more slowly 

 below. For fluids the rapid movement may be maintained even 

 in the lower part. 



In man and in the horse, fluids are shot into the oesophagus at 

 a velocity of several decimetres per second, owing to the impulse 

 from the rapid contraction of the mylohyoid muscles. Solids and 

 semi-solids are propelled slowly forward throughout the gullet by 

 peristalsis only, and Kronecker's theory is therefore justified in 

 regard to the deglutition of liquids and pulp ; but for the degluti- 

 tion of solids and semi-solids the old doctrine of peristalsis still 

 holds, although it must be understood in the restricted sense 

 imposed by the experiments of Kronecker and Meltzer. 



The later work of Zwaardemaker and Eykman, Schreiter, 

 Kindermann and Kahn has not contributed anything really new 

 to the subject. 



IV. Deglutition is a characteristically reflex act. It is true 

 that it commences as a voluntary process, but this, which Magendie 

 regards as the first period of deglutition, during which the bolus 

 reaches the isthmus of the fauces, has nothing to do with the act 

 of deglutition proper and may be logically regarded as the final 

 moment of mastication (Morat and Aiioing, 1880). Magendie 

 devised the following experiment in order to demonstrate the 

 necessity of the peripheral stimulus i.e. the bolus or fluid to 

 the act of deglutition : 



" Cherchez," he said, " a executer de suite cinq ou six mouve- 

 ments de deglutition, dans lesquels on avalera la salive contenue 

 dans la bouche : le premier et merue le second se feront facile- 

 ment ; le troisieme sera plus difficile, car il ne restera que tres peu 

 de salive a avaler ; le quatrieme ne pourra etre execute qu'au bout 



