424 A MANUAL OF PHYSIOLOGY 



The tubes to which the smallest amounts of saliva were added will 

 probably still show a distinct blue colour, while those at the other 

 end of the series will be brown or yellow, and the intermediate tubes 

 bluish- violet. Suppose D is the last tube still showing a bluish tint, 

 then in the next higher tube, C, all the starch has been hydrolysed 

 at least to dextrin that is, 1-3 c.c. of the ten -times diluted saliva, 

 or 0-13 of the original saliva, has been sufficient to change all the 

 starch in 10 c.c. of the i per cent, solution. With another specimen 

 of saliva the same result might be reached in tube E, containing an 

 amount of ferment equal to that in 0-06 c.c. of the original saliva. 

 We could then conclude that the diastatic power of the second saliva 

 was about twice as great as that of the first. A closer approximation 

 can now be made by setting up two fresh tubes (C and E respec- 

 tively for the two salivas) and determining the time required for the 

 blue reaction with iodine to disappear, taking out a drop from time 

 to time and testing on a porcelain slab. 



(i] Put a little distilled water into a porcelain capsule, and bring 

 the water to the boil. Now put into the mouth some boiled starch 

 paste, and move it about as in mastication. After half a minute spit 

 the starch out into the boiling water. Divide the water into two 

 portions. Test one for sugar, and the other for starch. Repeat the 

 experiment, but keep the starch two minutes in the mouth. Report 

 the result. 



(;) Starch solution to which saliva has been added is placed in a 

 dialyser tube of parchment-paper for twenty-four hours. At the end 

 of that time the dialysate (the surrounding water) should be tested 

 for sugar and for starch. Sugar will probably be found, but no 

 starch. If no reaction for sugar is obtained, the dialysate should 

 be concentrated on the water-bath, and again tested. 



2. Stimulation of the Chorda Tympani. (i) Having previously 

 studied the anatomy of the mouth and submaxillary region in the 

 dog by dissecting a dead animal (Fig. 157), put a good-sized dog 

 under morphine. Set up an induction-machine for a tetanizing 

 current (p. 184), and connect it with fine electrodes. Fasten the 

 dog on the holder, give ether if necessary, and insert a cannula in 

 the trachea (p. 186). Then make an incision 3 or 4 inches long 

 through skin and platysma muscle, along the inner border of the 

 lower jaw beginning about the angle of the mouth, and continuing 

 backwards towards the angle of the jaw. Such branches of the 

 jugular vein as come in the way may be generally pushed aside, but 

 if necessary they may be doubly ligated and divided. Feel for the 

 facial artery, so as to be able to avoid it. Divide the digastric muscle 

 about its anterior third, and clear it carefully from its attachments ; 

 or, without dividing it, pull it outwards with a hook. The broad, 

 thin mylo-hyoid muscle will now be seen with its motor nerve lying 

 on it. Divide the muscle about its middle at right angles to its 

 fibres, and raise it carefully. The lingual nerve will be seen emerging 

 from under the ramus of the jaw. It runs transversely towards the 

 middle line, and then, bending on itself, passes forwards parallel to 

 the larger hypoglossal nerve. In its transverse course the lingual 

 will be seen to cross the ducts of the submaxillary and sublingual 

 glands. These structures having been identified, the lingual nerve 

 is to be ligatured before it enters the tongue and cut peripherally to 

 the ligature. Then a glass cannula of suitable size is to be inserted 

 into the submaxillary duct (the larger of the two), just as if it were 

 a bloodvessel (p. 55). A short piece of narrow rubber tubing is care- 



