218 PKACTICAL PHYSIOLOGY 



EXPERIMENT IY. Add to some saliva in a test-tube a drop of a 

 weak solution of ferric chloride (Liq. Ferri. Perchlor. B.P.). A red 

 colour is produced due to the production of ferric sulphocyanide, the 

 ferric chloride reacting with a sulphocyanide (viz. KCNS) which is 

 contained in saliva. The red colour is discharged by adding a few 

 drops of a solution of mercuric chloride (1-1000). 



EXPERIMENT V. If some saliva be allowed to stand for an hour or 

 so it becomes milky or a thin surface film forms on it. This is due to 

 the precipitation of calcium carbonate which exists in fresh saliva as 

 calcium, bi-carbonate, which is soluble. On standing exposed to the 

 air, however, carbonic acid gas is given off, in consequence of which the 

 bi-carbonate changes into the carbonate. 1 A similar precipitation of 

 calcium carbonate carrying with it a certain amount of calcium 

 phosphate (Ca 3 (P0 4 ) 2 ) sometimes occurs in the ducts of the glands 

 and leads to the formation of calculi, or a similar precipitate may 

 form on the teeth, where it leads to the formation of tartar. 



II. To Study the Action of the Ferment Ptyalin. 



EXPERIMENT YL Place a few cubic centimetres of a 0*5 per cent, solu- 

 tion of starch in two test tubes, a and b. To b add about an equal amount 

 of saliva and place both in the water-bath heated to body temperature. 

 By means of a glass rod transfer drops from each solution about once a. 

 minute to a white slab and add to each drop a little iodine solution. In 

 the case of the test tube b the blue colour becomes at first purplish and 

 then reddish brown, and ultimately disappears. When this stage has 

 been reached apply Trommer's or Fehling's test to the contents of the 

 test tube, and note that reduction occurs. In the case of a the blue 

 colour persists throughout and reduction of cupric salts does not occur. 



What has occurred in b is that the ptyalin has hydrolysed the poly- 

 saccharide starch (blue with iodine and no reducing power), first into a 

 simpler polysaccharide dextrin (red with iodine, no reducing power), 

 and then into the disaccharide maltose (no colour with iodine, reduces 

 cupric salts). If left in contact with the maltose for some time the 

 ptyalin can invert this, yielding dextrose. There are really two forms, 

 of dextrin formed, the one which gives the iodine reaction described 

 above is called erythro-dextrin, but there is another achroo-dextrin 

 which gives no reaction with iodine. The latter exists as an inter- 

 mediate stage between erythro-dextrin and maltose. 



EXPERIMENT VII. Place some of 0-5 per cent, solution of starch in 



1 2CaH 2 (C0 3 ) 2 =2CaC0 3 

 (soluble) (insoluble) 



