554 PHYSIOLOGY OF THE DOMESTIC ANIMALS. 



ensue. The arterioles will now all dilate, and, as a consequence, the part's 

 will become filled with blood. 



Similar effects may be seen in warm-blooded animals. If the sympa- 

 thetic nerve be divided in the neck of a rabbit, it will be found that the 

 vessels in the lobe of the ear on that side will have greatly increased in 

 calibre, will appear not only larger, but numerous vessels which before 

 were invisible will now be readily seen. The entire tissue of the ear will 

 be much redder than before, much warmer in temperature, and distinct 

 throbbing of the pulse may be readily perceived. Here division of the 

 sympathetic has produced dilatation of the auricular arterioles. If, on 

 the other hand, the cervical sympathetic be stimulated with an induction 

 current in the rabbit, directly opposite results will be produced. The 

 auricular vessels will now all contract, and the tissues of the ear will 

 become pale and free from blood. 



So, also, if the sciatic nerve be divided in a mammal, a corresponding 

 dilatation occurs in the small arterioles of the foot and leg, and may be 

 readily determined through inspection of the balls of the toes, especially 

 as seen in the cat, where they are hairless and not pigmented. So, also, 

 the temperature of the foot on the side on which division of the sciatic 

 nerve has been performed will be considerably elevated. Further, if the 

 splanchnic nerves be divided, the vessels of the abdomen all undergo 

 extensive dilatation. If the lingual nerve be divided, the vessels on the 

 corresponding side of the tongue dilate, while in all cases in which 

 a nerve supplying a muscle is cut a great increase in the flow, of blood 

 from the muscle may be made out. It is, therefore, evident that the 

 blood-vessels of certain parts of the body are kept in a state of tonic 

 contraction through impulses traveling along certain nerves. Section of 

 these nerves has been found to produce dilatation in the corresponding 

 vascular areas : therefore it is evident that the arteries before the division 

 of their vascular nerves were in a state of constriction through contraction 

 of their muscular fibres, and that this state of contraction was due to 

 impulses coming along the vascular nerves or vaso-motor nerves of that 

 part. Section of these nerves, therefore, produces paralysis of the 

 muscular fibres, and the muscular tissue is no longer able to resist the 

 pressure of the blood, and, as a consequence, these vessels passively 

 dilate. 



It has been found that the vascular condition of the specific parts 

 of the body are governed by impulses coming along specific nerves, and 

 that these nerves may be either of the sympathetic or cerebro-spinal 

 systems. If the spinal cord is divided in the lumbar region it will be 

 found that the blood-vessels of all the parts below will be paralyzed and 

 gorged with blood. If the spinal cord, or even the lateral columns alone, 

 be divided in the cervical region, the blood-vessels of the entire body 



