1895 - 96 .] Dr Aitchi son Kobertson on Digestion of Starch. 97 
to 0*05 per cent, hydrochloric acid, the action of ptyalin is 
restrained. 
I performed similar experiments with the gastric fluid from a 
case of chronic gastric catarrh , the acidity of which was equal to 
0*067 per cent, hydrochloric acid. 
10 c.c. unhealthy gastric fluid, \ Acidity /Starch unchanged 
10 c.c. 1 % starch solution, > =0'022 % < after two hours 
10 c.c. saliva, ) HC1. • at 38° C. 
After being neutralised, however, the starch was completely con- 
verted within ten minutes, and the reducing substances present 
amounted to 0'23 per cent. 
Does the acid merely restrain, or does it actually kill the 
ptyalin ferment, if exposed long enough to its influence? 
By some authors it is affirmed that the former alone occurs, and 
that the conversive action of ptyalin again becomes potent on the 
gastric contents becoming alkaline after passing into the intestine. 
Others, again, state that the ferment is actually killed during its 
stay in the stomach. 
Outside of the body I found that the following takes place. 
I placed in a vessel 
10 c.c. gastric fluid (of acidity = 0*102 °/ Q HC1), \ ^ gg° q f or 
10 c.c. 1 % starch solution, > one } 10ur> 
10 c.c. saliva, * 
At the end of an hour the starch had undergone no conversion. 
I then carefully neutralised the mixture and kept it at 38° C. for 
thirty minutes. It was then found to contain much erythro- 
dextrin, soluble starch, and some unchanged starch. Substances 
reducing Fehling’s solution amounted to 0*19 per cent. 
In another experiment I left a similar mixture at a temperature 
of 38° C. for twenty-four hours before neutralising it. At the end 
of this period the starch had undergone no conversion. It was 
then neutralised and kept at the same temperature for thirty 
minutes, at the end of which time it contained much unchanged 
starch, some soluble starch and erythrodextrin, and 0*09 per cent, 
of reducing substances. After being kept in the warm chamber 
for two hours, it gave no coloration with iodine (showing that the 
YOL. XXI. G 
