194 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



the left cervical sympathetic is cut in a dog, and the animal is kept in his 

 kennel, (he left ear will always be found to be 5° to 9° warmer than the 

 right, [f the dog is now taken out for a run in the warm sunshine, and 

 allowed to heat himself until he begins to pant witli outstretched tongue, the 

 temperature of both ears will lie found to have increased. The right ear is 

 now, however, the warmer of the two, being from 1° to 5° warmer than the 

 left. The blood-vessels of the right ear are, moreover, now fuller than those 

 of the left. When the animal is quiet again the former condition returns, the 

 redness and warmth in the right becoming again less than in the left ear. The 

 increase of the redness and warmth of the right ear over the left, in which the 

 vaso-constrictor nerves were paralyzed, must be the result of a dilatation of 

 the vessels of the right ear by some nervous mechanism. For if the dilatation 

 of the vessels was merely passive, the vessels in the right ear cotdd not dilate to 

 a greater degree than those in the left ear which had been left in a passive state 

 by the section of their nerves. This experiment, however, is by no means con- 

 el nsive. 



The existence of vaso-dilator fibres was placed beyond doubt by the follow- 

 ing experiment of Bernard on the chorda tympani nerve, new facts regarding 

 the vaso-constrietor nerves being also secured. Bernard exposed the submax- 

 illary gland of a digesting dog, removed the digastric muscle, isolated the 

 nerves going to the gland, introduced a tube into the duct, and, finally, sought 

 out aud opened the submaxillary vein. The blood contained in the vein was 

 dark. The nerve-branch coming to the gland from the sympathetic w T as now 

 ligated, whereupon the venous blood from the gland grew red and flowed more 

 abundantly; no saliva was excreted. The sympathetic nerve was now stimu- 

 lated between the ligature and the gland. At this the blood in the vein became 

 dark again, flowed in less abundance and finally stopped entirely. On allow- 

 ing the animal to rest the venous blood grew red once more. The chorda 

 tympani nerve, coming from the lingual nerve, was now ligated, and the end 

 in connection with the gland stimulated. Then almost at once saliva streamed 

 into tiie duct, and large quantities of bright scarlet blood flowed from the vein 

 in jets, synchronous with the pulse. 



This experiment may be .-aid to close the earlier history of the vaso-motor 

 oerves. It was now established beyond question that the size of the blood- 

 vessels, and thus the quantity of blood carried by them to different parts of the 

 body, is controlled by nerves which when stimulated either narrow the blood 

 vessels (vaso-constrictor aerves) and thus diminish the quantity of blood that 

 (lows through them, or dilate the vessels (vaso-dilator nerves) and increase the 

 flow. The section of vaso-constrictor nerves, for example those found in the 

 cervical sympathetic, causes the vessels previously constricted by them to dilate. 

 The section of a vaso-dilator nerve, for example the chorda tympani, running 

 from the lingual nerve to the submaxillary gland, does not. however, cause the 

 constriction of the vessels to which it is distributed. And finally, it was now 

 determined that vaso-motor fibres are found in the sympathetic system as 

 well as in the spinal cord and the cerebro-spinal nerves. 



