48 CHEMICAL PHYSIOLOGY. 



to potassic sulpho-cyanide. The colour is discharged by 

 mercuric chloride. Meconic acid yields a similar colour, but 

 it is not discharged by mercuric chloride. The sulpho- 

 cyanide is present only in parotid saliva, and is generally 

 present in mixed saliva. 



(/.) Test a very dilute solution of potassic sulpho-cyanide 

 to compare with (e.) 



(g.) The salts are tested for in the usual way (see 

 " Urine "). Test for chlorides (HISrO 3 , and AglS"O 3 ), car- 

 bonates (acetic acid), and sulphates (barium nitrate and 

 nitric acid). 



3. Digestive Action. 



Starch Solution. Place 1 grm. of starch in a mortar, add a 

 few cc. of cold water, and mix well with the starch. Add 200 cc. 

 of boiling water, stirring all the while. Boil the fluid in a flask 

 for a few minutes. This gives a half per cent, solution. Do the 

 tests for starch already described (Lesson II., 2), and especially 

 satisfy yourself that no glucose or reducing sugar is present. 



Action of Saliva on Starch. 



(a.) Dilute the saliva with 5 volumes of water. Label 

 three test-tubes A, B, and C. In A place starch mucilage, 

 in B saliva, and in 1 volume of saliva and 3 volumes of 

 starch mucilage. Plug all three with cotton-wool, and place 

 them in a water-bath at 40 C., and leave them there for 

 ten minutes. Test for a reducing sugar in portions of all 

 three, by means of Fehling's solution. A and B give no 

 evidence of sugar, while C reduces the Fehling, giving a 

 yellow or red deposit of cuprous oxide. Therefore, starch 

 is converted into a reducing sugar by the saliva. This is 

 done by the ferment ptyalin contained in it. 



(b.) Test a portion of C with solution of iodine ; no blue 

 colour is obtained, as all the starch has disappeared, being 

 converted into a reducing sugar or maltose. 



(c.) Make a thick starch mucilage, place some in test- 

 tubes labelled A and B. Keep A for comparison, and to B 

 add saliva, and expose both to 40 0. Notice that A is un- 

 affected, while B soon becomes fluid within two minutes 



