216 UNCONSCIOUS NERVOUS OPERATIONS 



in a flask and allow it to stand several hours, shaking it occasion- 

 ally. Filter and test the nitrate for proteids, as in Ex. 91, and for 

 sugar as in Ex. 96. 



103. Shake some flour with ether in a test tube and allow it to 

 stand for an hour or two, keeping the tube tightly corked and shak- 

 ing it occasionally. Filter off the ether and place some of it on a clean 

 glass surface and allow it to evaporate. A greasy residue remains, 

 showing that the flour contained fat, some of which was dissolved out 

 by the ether. 



104. Gluten. Moisten flour with water till it forms a tenacious 

 dough. Tie it in muslin cloth and knead it in a vessel of water till 

 all the starch is separated. There remains in the cloth a sticky, elas- 

 tic mass of gluten, consisting of the insoluble albumins, some of the 

 ash, and the fats. Draw out some of the gluten into threads, and 

 notice its tenacity. 



105. Milk. Examine with the microscope a drop of fresh milk. 

 It is seen to be an emulsion of oil globules floating in a liquid. 



106. Warm some milk in a flask, and add a few drops of acetic 

 acid. The mass clots and separates into a solid curd, consisting of 

 casein and fat, and a liquid, the whey. Caseinogen is the chief proteid 

 of milk. In curdling it is changed to casein. 



107. Dilute milk with ten times its volume of water and slowly add 

 dilute acetic acid. As long as the liquid remains alkaline, or neutral, 

 as can be tested with litmus paper, no visible change occurs, but 

 on adding more and more of the acid there is finally formed a precipi- 

 tate of casein which, as in the preceding experiments, carries with it 

 most of the fat. 



108. Filter the curd from the whey obtained in one of the preced- 

 ing experiments, and test the filtrate for sugar (milk sugar) and pro- 

 teids (see Exs. 96 and 91). 



109. Test, with litmus paper, some perfectly fresh milk. It will 

 be found to be neutral, or alkaline. Allow it to stand in a warm place 

 till it becomes sour and curdles. It will be found to be acid in reac- 

 tion. In the souring of milk the milk sugar changes to lactic acid, 

 and curdling is finally produced by the acid, as was illustrated in 

 preceding experiments. 



110. Lean Meat. Mince finely some perfectly fresh muscles of a 

 cat, dog, or rabbit. Place them in a large jar of water and stir. Tn 

 about a quarter of an hour filter through muslin and place the muscle 



