226 PRACTICAL PHYSIOLOGY 



drop or so of a mixture of 5 parts sulphuric acid (cone.) and 1 

 part of water to run under the cover slip. Note that the edges of 

 the crystals become red. Now run in a drop of iodine solution, 

 when it will be noted that a play of colours results (brown, violet, 

 blue, etc.). 



Other colour reactions can be obtained with solutions of 

 cholesterol. 



EXPERIMENT X. Dissolve some cholesterol crystals in a few c.c. 

 of anhydrous chloroform, and add an equal volume of sulphuric 

 acid (cone.). Shake gently. On settling, it will be seen that the 

 chloroformic solution becomes coloured blood red and afterwards 

 purple, and the sulphuric acid shows a green fluorescence. If the 

 chloroform solution be moistened with water, as by pouring it into a 

 moistened test tube, the colour disappears. (Salkowski's reaction.) 



EXPERIMENT XI. Dissolve some cholesterol in anhydrous acetic 

 anhydride, and, after cooling, add some sulphuric acid (cone.). 

 A play of colours results. (Liebermann's reaction.) 



CHAPTER VIII 

 DIGESTION IN THE MOUTH AND STOMACH 



Saliva 



The salivary glands parotid, subliiigual and submaxillary 

 along with the numerous isolated gland acini scattered in the buccal 

 mucosa, pour into the mouth a secretion known as saliva. The 

 composition of this mixed saliva is as follows : 



Water 9942 per cent. 



Organic matter ...... 0-36 ., 



Mucus and epithelial cells. Ptyalin and soluble protein. 



Potassium sulphocyanide (KCNS). 

 Inorganic matter ...... 0-22 ,, 



Chlorides, phosphates, and carbonates of alkalies and alkaline earths. 



It is, therefore, a very dilute secretion (specific gravity about 

 1,005). 



The total secretion during twenty-four hours amounts to about 

 the same as that of the urine, i.e. 1,500 c.c. 



Collect some saliva in a test tube, 1 and perform the following 

 reactions with it : 



I. To Identify the Various Constituents. 



EXPERIMENT I. Place a drop of saliva on red litmus paper ; a 

 blue stain results. The reaction may, however, become acid where 

 decomposition is taking place in the mouth, as is the case in 

 decaying teeth. 



EXPERIMENT II. Place a drop of saliva on a slide, cover and 



1 The secretion of saliva may be stimulated by inhaling acetic acid through 

 the mouth, or by chewing rubber. 



