378 FOOD AND DIGESTION 



Anesthetize a dog and bind it to a suitable holder. Expose the nerves to 

 the submaxillary gland as follows: cut through the skin of the lower jaw 

 along the inner border for about 3 inches. Isolate and double ligate the 

 jugular vein and any other veins in the field except the ones coming from the 

 submaxillary 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 

 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. 



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 , 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. 6, 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. 



