158 PHYSIOLOGY CHAP. 



tinned for three days at body temperature, produced sugar, 

 both from animal starch (glycogen) and from vegetable starch 

 (potato) ; the whole of the maltose was split into two molecules of 



glucose. 



Surprising as is the readiness with which ptyalin acts upon 

 cooked starch, the time of its action is very short, and incom- 

 parably less in intensity than that of the analogous enzyme of 

 pancreatic juice. 



Recent 'researches prove that salivary digestion has a much 

 greater importance than was formerly supposed. 



J. Miiller (1901), e.g., found that saliva converts 50-70 per cent 

 and even more of the alimentary starches into soluble products 

 closely related to maltose. In cases of weak acid secretions in the 

 stomach, only very minute fractions of starch, as a rule, remain 

 undissolved. The saccharification of starch is therefore most 

 intense at the commencement of gastric digestion. Gaudenz 

 (1901), too, found that in the ingestion of starchy foods, such an 

 amount of saliva was secreted even after half a minute that it 

 induces a peculiarly energetic process of saccharification, and is 

 capable of dissolving large quantities of vegetable foods like 

 macaroni, potatoes, turnips, etc., while animal foods are only 

 dissolved to the extent in which they contain substances soluble 



in water. 



The saliva of carnivora, although it is secreted in great 

 quantities, is entirely destitute of ptyalin, as might be expected 

 from teleological considerations. The saliva of infants, up to a 

 year old, is also lacking in ptyalin, and therefore in diastatic 

 properties (Schiff and others). This is the best proof that the 

 principal function of the saliva is mechanical, i.e. formation of the 

 bolus. It must, however, lie added that saliva by its alkalinity 

 also serves to protect the teeth from the corrosive action of acids, 

 which are readily formed in the mouth by the fermentation and 

 decomposition of alimentary residues. One argument in favour of 

 this theory of Bunge is the fact that Cetacea that live in water are 

 entirely destitute of salivary glands, which are rudimentary in the 

 Pinnipeda. The emulsifying action of saliva on fats claimed by 

 some authorities (Colin, Longet, Corona, Ellenberger, Hofmeister) 

 is due to the mucin which it contains. According to others, 

 saliva promotes gastric secretion when it reaches the stomach, by 

 its alkalinity (Strieker); but this fact is not conspicuous or 

 constant enough to render it of importance. Dogs are apparently 

 none the worse for the extirpation of all the salivary glands, aud 

 only require to drink more frequently than usual during their 

 meals (Fehr, 1862). 



III. The formation of the bolus is succeeded by the act of 

 Deglutition, which carries it from the mouth to the stomach, 

 through the pharynx and oesophagus. The analysis of the 



