6i2 A MANUAL OF PHYSIOLOGY . 



(2) Shake up some finely-grated cheese in a dry test-tube with 

 ether. Take off the ether with a pipette, and evaporate on a water- 

 bath till only a few drops remain. With a glass rod put a drop of the 

 ether on a piece of filter-paper. A greasy spot is left, showing that 

 fat is present. 



6. Flour. (i) Mix some wheat-flour with a little water into a 

 stiff dough. Let it stand for a few minutes at body-temperature 

 to facilitate the formation of gluten. Wrap a piece in cheese-cl9th, 

 forming a kind of bag, and knead it with the fingers in a capsule of 

 water. The starch grains come through the cheese-cloth. Pour 

 the water into a beaker. It is ooaque, and on standing the starch 

 grains sink to the bottom, (a) Test for starch with the iodine test, 

 and also examine microscopically. The grains are round, with a 

 central hilum, and are smaller than those of potato starch (p. n). 

 (b} Test for sugar by Trommer's test (p. 10). None is present 

 unless the flour has been made from inferior grain in which some 

 germination has taken place. 



(2) Go on kneading the dough till no more starch comes through. 

 The sticky mass which remains in the bag is a protein called gluten, 

 which is formed from certain globulins and other proteins in the flour 

 on addition of water. Oatmeal, ground rice, and other grains poor 

 in gluten-forming globulins do not form dough when mixed with water. 

 Suspend some of the gluten in water in a test -tube, and apply to it 

 the general protein colour tests (p. 7). 



7. Bread. (i) Rub up a small piece of the crumb of a stale loaf 

 in a mortar with water. Strain through cheese-cloth. The fluid 

 which passes through contains starch grains, (a) Filter it, and 

 test a portion of the filtrate for dextrose by Trommer's test. A 

 positive result is obtained. Test another portion with iodine for 

 erythrodextrin. (b) Test a portion of the residue of the bread 

 which has not passed through the cheese-cloth for protein by the 

 general protein tests e.g., the xanthoproteic or Millon's tests. 



(2) Repeat (i) using the crust of the bread. Both dextrose and 

 erythrodextrin are present in the cold-water extract, but the dextrose 

 is less plentiful than in the crumb, having been converted into 

 caramel in the baking. The sugar and dextrin are formed from the 

 starch of the flour by the ferments of the yeast employed to make the 

 bread rise. 



8. Variations in the Total Nitrogen (p. 535) and in the Quantity 

 of Urea Excreted, with Variations in the Amount of Proteins in the 

 Food. The student should put himself, or somebody else if he can, 

 for two days on a diet poor in proteins, then (after an interval of 

 forty-eight hours on his ordinary food) for two days on a diet rich 

 in proteins. A suitable table of diets will be supplied. The urine 

 should be collected on the six days of the period of experiment, on 

 the day before it begins, and on the day after it ends. Small 

 samples of the mixed urine of the twenty-four hours for each of 

 these eight days should be brought to the laboratory, and the 

 quantity of urea determined by the hypobromite method. The 

 volume of the urine passed in each interval of twenty-four hours 

 being known, the total excretion of urea for the twenty-four hours 

 can be calculated, and a curve plotted to show how it varies during 

 the period of experiment.* If sufficient time is available, the experi- 



* In 17 healthy students the average amount of urea excreted in twenty- 

 four hours on the ordinary diet was 29*51 grammes (minimum 19*35 

 grammes, maximum 46*007 grammes) ; on a diet poor in protein, average 



