Any crumbs that may be in the solution if colored orange 

 would indicate the presence of a proteid. The liquid por- 

 tion may not show as deep a color, indicating a lesser 

 amount in solution. 



94. Try the above tests hurriedly by dropping a little 

 iodine solution upon the bread. Similarly with the xan- 

 thoproteic test by letting a drop of nitric acid fall upon the 

 bread and then a drop of ammonia upon the spot already 

 covered by the nitric acid. 



95. Potato. Boil a small piece of potato in water and let 

 it cool. Divide the liquid into two parts. 



Test one portion for starch with the iodine solution. With- 

 out boiling, the starch might give no reaction as the gran- 

 ules are enclosed in a coating of cellulose. 



96. Apply the xanthoproteic test. Only a faint orange 

 color appears, indicating that very little proteid is present. 



VIII. 



97. Gastric Digestion. For laboratory purposes a di- 

 gestive extract is usually prepared by removing the gastric 

 mucosa from the cardiac portion of the stomach of some 

 dome.stic animal while the ferments are still active. The 

 cardiac portion of the stomach of the pig is perhaps more 

 commonly used and easily obtained from the .slaughter house. 

 The stomach of a cat or dog is equally useful and their 

 deaths can be timed according to their digestive activity and 

 the stomach obtained in a perfectly fresh condition. Ex- 

 tracts of considerable concentration may be made by any of 

 the three following methods. 



98. Formalin extract of pepsin. Remove the mucosa 

 from the cardiac half of the stomach and mince it very 

 finely with a chopping knife or meat grinder. Weigh the 

 mucosa and add to it twenty-five times its weight of a o. i % 



