254 The Physiological Role of Saliva 



may have a "water taste" (Zotterman, 1949 ; Liljestrand and Zotter- 

 man, 1954; Cohen, Hagiwara and Zotterman, 1955; Zotterman, 



1956). 



For the chemical breakdown of food by saliva oc-amylase or 

 ptyalin is mainly responsible. According to Bernfeld, Staub and 

 Fischer (1948) all the amylolytic activity of human saliva is due to 

 a-amylase. Most investigations dealing with the activity of this 

 enzyme have been carried out on saliva from human beings. The 

 saliva from some of the common experimental animals has, in fact, 

 a very low amylolytic power or none at all (see page 178). In most 

 experiments on humans and animals mixed saliva has been used but 

 in some investigations parotid saliva has been collected separately 

 and found to have a much greater activity, sometimes four to eight 

 times greater than the mixed sample (Evans, 191 3; Fischl and 

 Kahn, 1930; Basir and Ramabhadran, 1937; Schneyer, 1956). 



Ptyalin can be demonstrated in saliva from infants; the activity 

 is low, however, but increases during the first year to the level 

 found in saliva of adults (Nicory, 1922). In old age the activity is 

 much reduced. Meyer, Golden, Steiner and Necheles (1937) com- 

 pared the amylolytic power of saliva from a group with an average 

 age of 81 years with that of a group aged 25 years. The activity 

 was found to be about 30 times greater in the younger than in the 

 older group. The authors conclude that in old age the pancreas is 

 mainly responsible for the first steps in the hydrolysis of carbo- 

 hydrates. 



What is the importance of the salivary amylase particularly in 

 relationship to pancreatic amylase? In a patient with an oesophageal 

 stricture Bonsdorff (1931) investigated the absorption and utiliza- 

 tion of food rich in carbohydrates introduced through a gastric 

 fistula ; he found it to be unimpaired by the absence of saliva and 

 assumed this to be due to a compensatory hyperactivity of the 

 pancreas. Conversely, it has been stated that the amylolytic activity 

 of human parotid saliva may increase when the pancreatic function 

 is disturbed (Molnar and Ungar, 1931). In dogs it has been found 

 that ligation of the pancreatic ducts is followed by the appearance 

 of amylase in saliva, even when the amylase level of the blood is not 

 raised (Maj and Bonora, 1943). It is not known how these adjust- 

 ments are brought about. The mechanism may be the same as that 

 responsible for the adaptation of the salivary amylase concentration 

 to the diet which is assumed by many investigators to occur. 



