400 FOOD AND DIGESTION 



increased, but the increase lasts for only a few minutes. If the sympathetic 

 fibers are stimulated before the chorda, then the sympathetic secretion is 

 relatively less than if the order of stimulation is reversed. 



Connect the duct with a mercury manometer and record the secretion 

 pressure, compare with arterial blood pressure. It is often greater. Explain. 



During stimulation of the nerves, note the relative flow of blood through 

 the organ. During chorda stimulation the flow is increased; during sympa- 

 thetic stimulation it is decreased, as these nerves contain vaso-dilator and 

 vaso-constrictor fibers, respectively. 



Inject 5 milligrams of pilocarpine. This drug stimulates the secre- 

 tory nerve endings and thus causes a copious flow of saliva. 



3. Microscopic Changes in the Gland Cells. Make a histological 

 preparation (by any standard method of fixing and staining) of the submaxil- 

 lary gland of the cat, a, taken after a period of several hours' fasting when 

 the gland cells may be assumed to be at rest; and b, immediately after a period 

 of activity (from eating, or activity secured by the stimulation of the chorda 

 tympani) and note : a, The cells from the resting gland are relatively larger, 

 the nuclei are pushed back against the basement membrane, they have 

 sparsely sustaining protoplasm, and the cells are crowded with large gran- 

 ules, which in a fortunate preparation fill the entire cell. The outlines of the 

 cells are relatively indistinct and the lumen of the gland is small, b, The 

 cells of the active gland are relatively small, the nuclei are centrally placed, 

 the protoplasm stains more definitely, the granules are usually present but 

 limited to the side of the cell next to the lumen, the outlines of the cells are 

 distinct, and the lumen is often quite large. 



4. The Chemical Composition of Saliva. Collect several cubic cen- 

 timeters of saliva as follows: Wash the mouth thoroughly with water, then 

 induce secretion of saliva by chewing a bit of paraffin or a piece of thoroughly 

 washed rubber. The inhalation of ether vapor will often facilitate the reflex 

 secretion. One should avoid strong acids to induce secretion unless their 

 presence is to be taken into consideration afterward. Make the following 

 tests: 



Reaction. A slip of neutral litmus-paper when introduced into freshly 

 collected saliva, or for convenience simply held in the mouth during sali- 

 vary secretion, shows an alkaline reaction. 



Mucin. To 3 or 4 cc. of saliva add 2 per cent, acetic acid drop by drop 

 until distinct acidity is obtained. On stirring the saliva with a glass rod a 

 sticky mucin makes its appearance. 



Potassium Sulphocyanide. To 2 cc. of saliva in a test-tube add 2 or 3 

 drops of ferric chloride solution, slightly acidulated with hydrochloric acid, 

 a reddish-brown coloration indicates the presence of potassium sulpho- 

 cyanide. One should run a blank test on distilled water for comparison. 



