CHAP. II.] DESTRUCTION OF PTYALIN IN THE STOMACH. 157 



In connection with the neutralisation of saliva by acid we have 

 to consider "a point, concerning which there is a disagreement be- 

 tween Langley and Chittenden. It had been shewn by Danilewsky 1 

 that various proteids combine with acids and alkalies, or with one 

 of them, and Langley 2 found that in the case of saliva, because of the 

 proteids which it contains, a certain amount of acid may be added 

 without there being any acid free, because of the formation of 

 acid-proteid. Now, according to Langley, the acid-proteid which is 

 formed when saliva is neutralised with acids acts prejudicially on the 

 diastatic action of the salivary ferment, whilst according to Chit- 

 tenden and Smith 3 , the influence of ' acid-proteid matter ' seems to 

 stimulate the diastatic action, up to a certain point, larger quantities 

 ultimately slowing, and even destroying, the ferment. 



Summarising, then, the researches to which we have alluded we 

 may safely conclude that in the first stage of gastric digestion, i.e. 

 for a period up to about half-an-hour, the conversion of boiled starch 

 into dextrins and maltose doubtless proceeds actively, but that it 

 then ceases, under the influence of acid-proteids and free acid. 



is the sail- Closely connected with the question just discussed is 

 vary diastatic one to which we have incidentally referred, viz. whether 

 ferment de- the diastatic ferment is destroyed or not in the stomach. 



stomach ? n ^ ^P on t ^ 1 ^ s matter > ^ so > tne earlier statements of authors 

 differed very greatly. Thus it was said by Cohnheim 4 

 that the diastatic ferment is not destroyed when submitted to arti- 

 ficial digestion with pepsin and hydrochloric acid for many hours, for 

 on neutralising the liquid it was found to possess diastatic powers. 

 Schiff 5 made the same statement ; and more recently Defresne 8 has 

 repeated it. Roberts 7 , on the other hand, asserted that the diastatic 

 power of the saliva is quickly and permanently abolished both by 

 an artificial digestive fluid and by filtered gastric juice obtained 

 from the human stomach. On this subject we refer to the more 

 recent experiments of Chittenden and of Laugley, already referred 

 to, as furnishing us with the most valuable and reliable information, 

 and as proving conclusively the ultimate destruction of diastatic 

 ferment in the stomach. 



Changes in the Acidity of the Contents of the Stomach during 



Digestion. 



It has been already said that the acidity of the contents of the 

 stomach increases as digestion proceeds, and attention must now be 



1 Danilewsky, Centralblatt f. d. med. Wissenschaft, 1880, quoted by Langley. 



2 J. N. Langley and F. Eves, ' On certain conditions which influence the amylo- 

 lytic action of saliva.' Journal of Physiology, Vol. iv. p. 18. 



3 Chittenden and Smith, loc. cit. 



4 Cohnheim, ' Zur Kenntniss der zuckerbildenden Fermente.' Virchow's Archiv* 

 Vol. xxvni. (1863), p. 248. 



5 Schiff, Lemons sur la Digestion, Vol. i. p. 162. 



6 Defresne, ' Etudes comparatifs sur la ptyaline et la diastase.' Comptes Eendus, 

 Vol. LXXXIX. p. 1070. 



7 Eoberts, On the Digestive Ferments, &c. London and Manchester, 1880, p. 53. 



