THE MOUTH SWALLOWING.; SALIVARY DIGESTION 67 



There seem to be two phases in what is called the peristal- 

 tic wave. The eye detects chiefly the traveling contrac- 

 tion, but this is apparently preceded by a zone of unusual 

 relaxation, a region of inhibition. 



The peristaltic wave which is necessary for the propul- 

 sion of solid food does not seem to be required to send liquid 

 to the stomach. A swallow of water is shot swiftly from 

 the mouth to the cardiac sphincter and arrives there dis- 

 tinctly in advance of the plodding peristalsis. When one 

 drinks a glass of water, the swallows following in rapid suc- 

 cession, a single peristaltic wave ends the series. Of 

 course, when fluid is carried up-grade in the esophagus, as 

 when a horse is drinking from a pool at his feet, active 

 peristalsis is as necessary as though solid food were being 

 moved, and one may plainly see the passing of each swallow 

 along the extended neck. We shall find that the small 

 intestine exhibits movements which are approximately 

 the same in principle as those of the esophagus, but far 

 slower and usually less energetic. 



Salivary Digestion. Within the stomach the accumu- 

 lated food with a large admixture of saliva lies for some time 

 with little motion. Here then salivary digestion must take 

 place. The statement has been made that in some animals 

 the saliva has only mechanical and protective functions. 

 More frequently, however, it has the power to hydrolyze 

 starch, forming malt-sugar as the chief end-product. This 

 seems to justify the assumption that an enzyme is present, 

 and it is variously named ptyalin, salivary amylase, or 

 salivary diastase. Such an enzyme probably plays an im- 

 portant part in the digestive processes of ruminants, ani- 

 mals which chew the cud. Human saliva acts upon starch 

 with surprising energy. A simple demonstration of the 

 fact may be had by holding a bread-crumb in the mouth 

 longer than is habitual, when it will gradually develop a 

 mildly sweet taste. 



The prevailing opinion in regard to the amount of diges- 

 tion accomplished by the saliva in man has undergone a 

 change during the last few years. It is allowed a larger 



