Chittenden and Smith — Diastatic Action of Saliva. 373 



c. Destructive action of free acid. 



It has been clearly shown* that acid approximating to the strength 

 of the acid of the gasti'ic juice has a destructive action on the sali- 

 vary ferment. Smaller percentages of acid have a like destructive 

 action. It has at the same time been shown that the presence of very 

 much smaller percentages of free acid stops the amylolytic action of 

 the ferment. Is this stopping of the amylolytic action in every case 

 due to destruction of the ferment, or simply to the retarding action 

 of its presence ? Langley, by using an aqueous extract of the pa- 

 rotid of rabbits, with but little proteid matter, concluded that the 

 presence of 0*014 per cent, hydrochloric acid is sufficient to destroy 

 all but the merest trace of ferment in five minutes at 39° C. This 

 before the action of acid-proteids was known. Chittenden and Ely 

 by experimenting with human saliva came to the conclusion " that 

 there may be in the presence of a very dilute acid, a simple stopping 

 of the diastatic action, without destruction of the ferment ;" in other 

 words, the retarding influence of very small percentages of free acid is 

 not necessarily due to destruction of the ferment. Langley and Eves 

 criticising this conclusion state " that since Chittenden and Ely 

 apparently used unneutralized saliva and took no account of the 

 proteids present, it seems to us probable that not only was there 

 no free hydrochloric acid in their experiments, but that even the 

 proteids were not saturated with acid." In the article to which they 

 refer it is, however, explicitly stated in a foot notef that the saliva 

 was neutralized and then an amount of acid added to equal 0*025 per 

 cent. Unfortunately, we did not then know of the action of acid on 

 the proteids of the saliva ; consequently, the above percentage must 

 have been mainly in the form of combined acid. Still, the smaller 

 percentages of free acid do not show great destructive action ; their 

 power of retarding the action of the ferment is out of all proportion 

 to their power of destruction. Amylolytic action is almost entirely 

 stopped by the presence of 0*002 per cent, free hydrochloric acid, 

 but warming saliva at 40* C. with 0*002 or even 0*005 per cent, hy- 

 drochloric acid for 30 minutes causes little if any destruction of the 

 ferment. On neutralization, diastatic action goes on as vigorously as 

 ever. 



This is well illustrated by the following experiments: 



* Chittenden and G-riswold, loc. cit. ; Chittenden and Ely, loc. cit. ; Langley, loc. cit. 

 \ Amer. Chem. Jour., vol. iv, p. 119. 



