308 VETERINARY PHYSIOLOGY 



gullet. In this condition food is forced down entirely by the 

 pressure from the mouth. 



Fluids are normally shot right down the relaxed gullet by 

 the pressure from the mouth and from the constrictors. Less 

 fluid matter is passed down the oesophagus by a true peri- 

 stalsis — a zone of relaxation passing down in front of a zone 

 of contraction. This peristalsis is stopped for some time if the 

 vasfi nerves are cut and as a result food cannot be swallowed. 

 The vagus is the great efferent nerve for the reflex part of the 

 act of swallowing. But it has been found that, after the vagus 

 has been cut for twenty-four hours or more, distension of the 

 oesophagus by food may cause a peristalsis passing on to the 

 stomach. The peripheral nerve plexus in the wall of the 

 gullet must be capable of stimulation by such distension, and 

 it must be able, in these conditions, to initiate and to main- 

 tain peristalsis. 



Time of Swallowing. — Observations made on the human 

 subject by feeding with food impregnated with bismuth and 

 studying the changes in the oesophagus b}^ X-rays have shown 

 that fluids and solids, well masticated and mixed with saliva, 

 are passed rapidly down the gullet, reaching the orifice of the 

 stomach in about three seconds. Here they are delayed, 

 and do not pass into the stomach for another period of 

 about three seconds. Dry solids take much longer to pass 

 down the sruUet, sometimes as much as fifteen minutes. 



III DIGESTION IN THE STOMACH. 



Most important work on digestion in the stomach has 

 been accomplished by Pavlov on dogs. His method is 

 to make a small gastric pouch opening on the surface, 

 and separatee] from the rest of the stomach (fig. 150). 

 This is done by cutting out a V-shaped piece along the 

 great curvature, the apex being towards the pylorus and 

 the base being left connected with the stomacli wall. By 

 a series of stitches, the opening thus made in the stomach 

 is closed up (top line of XXs in fig. 150), while the cut 

 edges of the V-shaped flap are stitched together to form 



