172 SPECIAL PHYSIOLOGY 



(6) Subject bread to the xanthoproteic test. The presence of 

 proteid material is demonstrated. Put a small piece of dry bread 

 into a beaker with gastric juice and note effect. 



(c) Note the course of casein digestion. 



(d) Triturate in a mortar well-cooked lean meat ; digest with 

 gastric juice. 



(e) Try the xanthoproteic test upon cooked beans or peas; proteid 

 is present. Triturate in a mortar; digest. 



(/) In each case demonstrate the ultimate appearance of peptone. 



(14) The Artificial Digestion of Milk. Of fresh milk take three 

 portions of 5 c.c. each. 



(a) To one portion add ten volumes of artificial gastric juice and 

 place it in the incubator at 38 to 40 C. 



(6) Prepare another beaker in the same way, but place it in a 

 water-bath at 38 to 40 C. and keep the mixture well stirred, divid- 

 ing the casein coagulum as fine as possible. 



(c) Place the third portion of milk in the water bath. When it 

 has become warm add a few centimetres of rennin. Fifteen minutes 

 later add artificial gastric juice. Stir as in (b). In which of the first 

 two does digestion seem to progress the more rapidly? Does the 

 progress or process of the digestion seem to be materially different 

 in the last two experiments (6) and (c) ? Have any of the observations 

 made on milk digestion any hygienic significance? 



(15) The Diffusibility of the Products of the Artificial Digestion 

 of Proteids. From the products of digestion in experiments (14, 6) 

 digested milk, (13, a) digested gelatin, (13, 6) digested bread, fill 

 three dialyzers first neutralizing the acid with sodic carbonate. 

 After twelve to twenty-four hours, test the diffusate for peptone. 

 Why neutralize the liquid before filling the dialyzer? 



Have all of these indiffusible proteids been wholly or in part 

 changed to diffusible peptones by the action of the artificial gastric 

 juice? 



VIII. THE PROPERTIES OF FATS. 



1. Materials. Olive oil; cream; butter; beef -tallow; lard; adipose 

 tissue, and cotton-seed oil. 



2. Experiments and Observations. (1) The Osmic Acid Test. 

 Place in test-tubes a small amount of each of the above foodstuffs; 

 add to each a few cubic centimetres of osmic acid. A characteristic 

 reaction takes place, the result of which is a deep-brown coloration 

 of the fat. If the conditions are favorable the stain deepens into a 

 sepia black. The cream and the adipose tissue have proteid admix- 

 tures; note the variation of the reaction. 



(2) The Solubility of Fats and Oils. Prepare three tubes each of 

 olive oil and of tallow; treat each material with absolute alcohol, 

 with ether, and with chloroform. It will be found that all of these 



