166 A MANUAL OF VETERINARY PHYSIOLOGY 



on the other hand, all the herbivora are capable of digesting raw 

 starch, perhaps because they can digest cellulose. 



If boiled starch be mixed with filtered human saliva and 

 kept at a temperature of 95 ° R, in a short time the characteristic 

 reaction of a blue colour with iodine disappears, and a reddish 

 colour is formed on the addition of this reagent, indicating the 

 presence of a substance known as erythrodextrin. The fluid, 

 which before was sugar-free, contains distinct evidence of the 

 presence of this substance ; by continuing the action of the saliva 

 it is shortly found that the red colour on the addition of iodine 

 has disappeared, and the fluid gives evidence of containing a 

 considerable proportion of sugar. But analysis shows that for 

 the amount of starch employed the full amount of sugar has not 

 been obtained ; in other words, there is a second substance 

 present besides sugar, which is produced as the result of the 

 action of the saliva, and to this the name achroodextrin has been 

 given ; it is formed from erythrodextrin. The sugar formed 

 from starch by the action of saliva is not grape-sugar, but 

 maltose ; glucose (dextrose or grape-sugar) only being found in 

 small quantities, if at all. This action of the saliva on starch is 

 described as the Amylolytic action ; it is due to the presence of 

 ptyalin. 



Ptyalin, the active principle of starch-converting salivas, is 

 an unorganised enzyme, and, like all ferments, is of unknown 

 chemical nature. It is capable of converting cooked starch 

 rapidly and raw starch slowly into maltose and dextrin, the 

 ferment acting by hydrolysis ; viz., the molecule of starch takes 

 up water, and undergoes cleavage into simpler bodies. Between 

 starch and maltose there are doubtless many other bodies, but 

 the chemistry is not agreed upon. The amylolytic action is 

 permanently destroyed by a high, inhibited by a low tempera- 

 ture, retarded by a slightly acid or alkaline medium, and de- 

 stroyed by free hydrochloric acid. If starch be boiled with a 

 dilute acid, conversion into sugar occurs. The difference between 

 the action of boiling acid on starch and of saliva is that the latter 

 can only produce maltose, whereas the acid produces dextrose. 



The view we hold as to the non-amylolytic action of saliva 

 in herbivora is not supported by other observers ; Ellenberger* 

 distinctly states that both the parotid and submaxillary secre- 

 tions of the horse and ox can convert starch into sugar, but in 

 the case of the horse it is only the saliva first secreted by the glands 

 after a rest which possesses this property ; as secretion proceeds 

 the power is nearly lost. In the pig, according to this observer, 

 all the salivary glands are starch-converting ; in the rabbit the 

 submaxillary has no action, while the parotid is energetic ; in the 



* ' Physiologie der Haussaugethiere.' 



