766 THE VASOMOTOR CENTER AND NERVES. 



in a reflex way. Among poisons, almost all of the members of the digitalis- 

 group cause constriction. Quinin and salicin cause constriction of the vessels of 

 the spleen. The remaining febrifuges cause dilatation of the vessels, as does also 

 Witte's peptone. 



The influence of the vasomotor nerves upon the temperature, both of 

 limited portions of the body as well as of the entire body, is of great 

 significance. 



Local effects. Division of a peripheral vasomotor nerve, for ex- 

 ample the cervical sympathetic, causes dilatation of the vascular area 

 supplied by it, as the paralyzed vessels are readily distended by the 

 intra-arterial pressure. In consequence, a larger amount of arterial 

 blood at once enters this area, and as a result injection-redness develops, 

 and, at the same time, also in parts that readily become cool, such as 

 the ear and the skin of the face elevation of temperature. Increased 

 transudation takes place through the walls of the relaxed capillaries. 

 Within the dilated vessels the velocity of the blood-current is, naturally, 

 diminished, while the blood-pressure is increased. Further, the pulse 

 is more readily palpated in such situations, because the lumen of the 

 vessel is increased. With the increased size of the blood-current the 

 blood may be bright red as it enters the veins and the pulse may even be 

 followed into the veins. Every irritation of a peripheral vasomotor nerve 

 gives rise to the opposite phenomena, namely pallor, diminished trans- 

 udation and reduction in temperature in the external integument. 

 Smaller arteries become contracted to the point of complete disappear- 

 ance of their lumen. Long-continued irritation causes finally exhaus- 

 tion of the nerve and gives rise at the same time to symptoms of paralysis 

 of the vessel-wall. 



The phenomena described as following paralysis of vasomotor nerves do not, 

 however, remain unchanged. The paralysis of the muscular coat of the vessels 

 must obviously give rise to stagnation in the circulation of the blood, as the 

 muscular coat constitutes an important factor in the normal distribution of the 

 blood in the vessels. The slower blood-movement is responsible for the fact that 

 parts exposed to the air become more readily cooled. Thus, the primary stage 

 of elevation of temperature after division of the vasomotor nerves may be followed 

 by a second stage of reduction in temperature. As a result of numerous experi- 

 ments Landois was able to confirm the observation of Schiff that in rabbits from 

 which the cervical sympathetic had been removed some weeks previously, the 

 ear upon the intact side was always warmer, and particularly if the animals 

 were actively stimulated, in consequence of which the circulation in the intact 

 vessels was accelerated. If, as, for example, in the paralyzed extremities of 

 human beings, the muscle-nerves are paralyzed in addition to the vasomotors, 

 the extremity will become cooler in the course of time, because the paralyzed 

 muscles are no longer capable of generating heat by their contraction, and, 

 further, because the dilatation of the muscle- vessels, which occurs with each con- 

 traction of the muscles, is lost. If, finally, the paralyzed muscles undergo atrophy 

 the vessels contained in them also become reduced in size. There is thus afforded 

 an explanation for the fact that paralyzed extremities in human beings are as 

 a rule cold in the further course of the case, although primarily the temperature 

 is elevated. 



If in consequence of the same procedure the vasomotor nerves of 

 extensive areas of the skin are paralyzed, as, for example, in the lower 

 half of the body after section of the dorsal cord, so much heat is given 

 off by the dilated vessels that either an elevation of the temperature of 

 the skin is observed for only a short time and in slight degree or reduction 

 in temperature takes place at once. Thus, some observers have noted 

 elevation of temperature after division of the cervical cord, although 

 Riegel did not. 



