104 A Manual of Veterinary Physiology. 



starch in man and the dog-, and according to some observers 

 in horses and cattle, by the presence of ptyalin in the saliva. 



If boiled starch be mixed with filtered human saliva and 

 kept at a temperature of <).*> F., in a short time the charac- 

 teristic 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. At this time the fluid, which before was 

 sugar-free, now contains distinct evidence of its presence ; 

 by continuing the action of the saliva it is found that 

 shortly the red colour on the addition of iodine has dis- 

 appeared, and the fluid now contains a considerable propor- 

 tion of sugar. 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 in 

 addition to sugar as the result of the action of the saliva. 

 and this is described as achroodextrin. 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 which 

 acts the part of a ferment. The process is destroyed by a 

 high or low temperature, retarded by a slightly acid or 

 alkaline medium, and destroyed by free hydrochloric acid. 



If starch be boiled with a dilute acid conversion into 

 sugar occurs ; but the difference between the action of this 

 and saliva is, that whereas the latter can only produce 

 maltose the acid produces dextrose. 



The view 1 hold as to the non-amylolytic action of saliva 

 in herbivora is not supported by other observers. Ellen- 

 berger* distinctly states that both the parotid and sub- 

 maxillary saliva 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 gland after a rest, which possesses this 

 property to a high degree: as secretion proceeds the power 



* ' Physiologic der Hausaaugethiere.' 



