194 



Dr. A. Sheridan Lea. A comparative [Feb. 20, 



for the experiments deal chiefly -with the factors which determine the 

 activity of a ferment during digestion, and there is no reason for 

 supposing that there is any fundamental difference in the circum- 

 stances which may modify the activities of two ferments so closely 

 similar as those of the salivary gland and pancreas. Indeed, it 

 seems probable that what holds good for saliva will hold good with, 

 even greater force for the pancreatic ferment, since the latter is 

 relatively more active than the former. 



The experiments were conducted by comparing the products 

 formed when portions of the same mixture of starch and saliva are 

 simultaneously digested for equal times in (i) the dialyser, (ii) a 

 flask. The products with which I had to deal were dextrin and 

 maltose. These I estimated in each case as follows : — The dextrin 

 was precipitated by alcohol in excess, dried at 100°, and weighed ; 

 the alcoholic filtrate from this was evaporated to dryness, the residue 

 taken up in water, and the sugar determined in this by rotation and 

 reduction, and no results were accepted in which these two methods 

 did not give equivalent values for the sugar in solution. The 

 following experiments illustrate the accuracy obtainable by these 

 methods. 3*412 grams of starch were placed in each of two flasks 

 and digested with saliva. 



Flask 1. — 3*412 gr. starch yielded 0'505 gr. dextrin. 



2-838 gr. maltose. 



3'343 



Flash 2. — 3'412 gr. starch yielded 0-448 gr. dextrin. 



2- 904 gr. maltose. 



3- 352 



The results of my numerous experiments are as follows : — 



1. The rate of digestion, estimated by the times of relative dis- 

 appearance of the iodine reactions, is greater in the dialyser than in 

 a flask. 



2. The tendency to the development of bacteria is much less in the 

 dialyser than in a flask. 



3. The amount of starch finally converted into sugar is always 

 greater than in a flask, and the amount of dextrin residue is less. 



This is shown by the following typical experiment. 



Using a mixture of starch and saliva which contained 423 per 

 cent, of staich, at the end of twenty-one hours' digestion the dialyser 

 contained 16*78 per cent, dextrin, the flask 36'62 per cent. At the 

 end of sixty-eight hours the dialyser contained 8'48 per cent, of 

 dextrin, the flask 35*70 per cent. 



