352 FOOD AND DIGESTION 



maxillary gland. Isolate and cut the digastric muscle, also the mylo-hyoid, 

 using pains not to injure the duct of the gland or its arteries. When the 

 muscles are laid back, the artery and accompanying sympathetic nerve 

 branches, the hypoglossal and the lingual nerves, the submaxillary duct and 

 the submaxillary gland, will all be exposed. Isolate and introduce a very 

 fine glass cannula into the submaxillary duct. A small nerve filament 

 branches from the lingual nerve and runs to the hilus of the gland, the chorda 

 tympani. Carefully expose the chorda, place a silk ligature under it for con- 

 venience in handling. Also expose the sympathetic filaments with the artery. 



Stimulate the chorda tympani with a mild induction current for a few 

 minutes at a time at intervals, and note that the secretion which is absent 

 or forming slowly before stimulation now gathers quickly and leaves the end 

 of the cannula in a series of drops. Collect the saliva in a small beaker. One 

 can measure the rate of flow by collecting the saliva in a small graduated 

 cylinder, or, by changing the beaker every ten minutes, making a record of the 

 quantity of secretion formed. Stimulate the sympathetic fibers, cutting the 

 hypoglossal nerve if necessary, and note that the secretion is very slightly in- 

 creased, 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. 



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. 



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 5, 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. Z>, 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 



