374 PRACTICAL PHYSIOLOGY 



tion and swallowing of others. A body must be in solution before it can be 

 tasted, so that the saliva assists in the appreciation of taste. It is also 

 necessary for articulation and for preserving the sensitiveness of the 

 nerve endings of taste and common sensation. This explains why a 

 fever patient cannot taste things so well as during health. It is inter- 

 esting to note that in some animals the saliva contains little or no 

 amylolytic ferment (e.g. dog and cat). 



For accurately studying the action of ptyalin (or any other amylolytic ferment) 

 on starch one may estimate the reducing power (Bang's method, gravimetric 

 method, polarimeter) of the incubated solution after a certain time. Besides being 

 tedious, this method is uncertain, because of the different reducing powers of 

 maltose and dextrose, both of which sugars frequently result by salivary digestion, 

 especially when this is prolonged. 



A simpler and more serviceable method depends on the colour reaction of 

 starch with iodine, and is conducted as follows : 



Prepare a 1 per cent, starch paste solution, 1 and place the beaker containing it in 

 ice water. Collect some saliva and dilute 1 c.c. of it to 10 c.c. with distilled water, 

 and filter. Take a series of five test tubes labelled A , B, C, etc. , and with a 1 c. c. 

 pipette graduated in 100 parts deliver into tube A 1 c.c. of the diluted saliva ; 

 into B 0-75 c.c.; into C 0'5 ; into D 0'25 ; and into E O'l. 



Place the tubes in a beaker containing ice water, and then deliver into each 5 c.c. 

 of 1 per cent, cooled starch solution. The cold prevents any ferment action until 

 all are ready. Now remove the tubes to another beaker containing water at 

 40 C. , and gently shake them so that the contents become thoroughly mixed. Note 

 the exact time at which the tubes are placed in the warm water. At the end of 

 half an hour remove the tubes simultaneously to ice water, and shake them gently 

 so as to ensure thorough cooling. Fill each tube to within half an inch of the top 



/ N \ 

 with distilled water and add a few drops of iodine solution ( TTJ )- 2 Close each 



tube with the finger and invert so as to mix. It will be seen that there is a grada- 

 tion of colours in the different tubes from blue through violet and brown to yellow. 

 Note the tube which just shows a bluish tint. The next one higher up in the 

 series is taken as that in which all starch has just disappeared. From the amount 

 of diluted solution added to this, calculate the amount of undiluted saliva required to 

 convert 100 c.c. of 1 per cent, starch solution into dextrines in half an hour at 40 C. 

 Thus, suppose that the tube containing 0'25 c.c. diluted saliva is found to be that 

 which just shows a bluish tint. In the next (viz. containing 0'5 c.c. saliva) all 



the starch has disappeared, therefore -TTT- = '05 c.c. saliva can hydrolyse 5 c.c. 

 1 per cent, starch, or 1 c.c. can invert 100 c.c. 1 per cent, starch. Thediastatic action 



1 Weigh 1 or 2 gm. of pulverized " soluble starch," and stir it up in a beaker 

 with an amount of distilled water sufficient to make a 1 per cent, solution. Place 

 on a boiling water bath and continue stirring until a clear opalescent solution is 

 obtained. Cool before using. 



2 Care must be taken that sufficient iodine solution is added to give the 

 maximal reaction, but an excess must be avoided. The iodine solution is made 

 by dissolving 12'7 gr. iodine in water containing 25 gr. potassium iodide, and 

 then diluting to 1000 c.c. 



