106 A Manual of Veterinary Physiology. 



ing the submaxillary gland is a branch of the sympathetic, 

 which spreads out and invests with constrictor tibres the 

 walls of the artery supplying the part. 



Thus the chorda tympani supplies the gland with secre- 

 tory fibres, and the walls of the vessels with dilator tibres, 

 whilst the sympathetic supplies the vessels with constrictor 

 fibres, and only a few secretory fibres. 



If the chorda be stimulated the vessels dilate, the gland 

 becomes red, the blood flowing from the veins is arterial in 

 tint, and the veins pulsate. In addition to this, there is an 

 abundant secretion of watery saliva poor in solids. When 

 the sympathetic is stimulated the vessels contract, only a 

 small quantity of extremely viscid saliva flows which is 

 rich in solids, the blood in the veins becomes very dark 

 in colour, and the blood-stream slows. 



That the increased flow of blood to the gland produced 

 by irritating the chorda does not produce the secretion, is 

 proved by the fact that the pressure of the saliva in the 

 duct of the gland is higher than the blood pressure outside 

 the gland. Further, if before stimulating the chorda some 

 atropine be injected, stimulation of the nerve still produces 

 to the full all the vascular changes, but not a trace of 

 saliva is secreted. Hence, secretion is not due merely to 

 increased blood pressure. 



This atropine experiment proves the existence in the 

 chorda of the two sets of nerves, viz., of the secretory and the 

 vaso-dilator. Through the atropine the secretory are 

 paralysed, the dilators are not. Atropine does not affect 

 the action of the sympathetic nerve. 



Twenty-four hours after the chorda has been divided ;i 

 watery secretion occurs, not only on the side operated upon 

 but on the opposite side also; this has been termed paralytic 

 secretion, it diminishes about the eighth day. 



Though the action of the nerves on the submaxillary 

 gland is universally accepted, great difference of opinion 

 exists as to how they act. Heidenhain's view is that a gland 

 is supplied with a trophic nerve which excites chemical 

 changes in the protoplasm, and a secretory nerve which 



