CHAPTER XXIV 

 Mechanism of Secretion 



THE process of secretion may be studied in the salivary glands, the 

 pancreas, the kidneys, and the mamma. The influence of nerves upon 

 secretion is illustrated by the salivary glands, that of hormones by 

 the pancreas and mamma. The secretion of the kidneys is also 

 dependent partly upon chemical agents, but largely upon the blood- 

 pressure and blood-flo\v through the organ. The following experiments 

 are suitable for demonstration. 



The submaxillary gland. A dog, having been anaesthetised, is 

 fixed on its back and a vein-cannula inserted into a saphenous vein. 

 An incision is then made on one side through the skin and fascia 

 below the mouth, extending from the chin backwards for 3 or 4 

 inches nearly parallel with the line of the lower jaw. At the posterior 

 part of the wound the submaxillary gland may be observed. The 

 anterior belly of the digastric, which comes into view and conceals 

 the hilum of the gland, is drawn over laterally by a weighted hook : 

 or it may be cut away. Any oozing from small vessels is controlled 

 by rinsing the wound with dilute extract of suprarenal ; larger vessels 

 are tied. A muscle the geniohyoid is now exposed : it is composed 

 of transverse fibres. When it is cautiously cut through, the duct of 

 the submaxillary gland (Wharton's duct) is seen passing obliquely 

 forwards towards the floor of the mouth. It is accompanied by 

 a smaller duct, that of the sublingual. Crossing these ducts is a con- 

 spicuous nerve the lingual branch of the 5th. If this is drawn 

 towards the middle line with a blunt hook, it is seen that just before 

 it crosses the ducts it gives off a small nerve the chorda tympani 

 which curves sharply backwards and enters the hilum of the sub- 

 maxillary gland, whence the duct is emerging. Tie a thread around 

 the lingual above the place where the chorda leaves it, and, without 

 injuring it, clear a short length of the chorda so that a small pair 

 of flat electrodes can be placed underneath it. Stimulate by induction 

 shocks : the duct will fill with saliva. 



Place a wet thread round the duct and slip a pointed piece of 

 paraffined paper under it. Make a snip into it with fine scissors ; 



