768 THE VASOMOTOR CENTER AND NERVES. 



blood-stream, with increase in the weight of the body. Such a result is brought 

 about by a number of poisons, for example alcohol in large doses. After disappear- 

 ance of the intoxication the normal weight is restored after copious urination. 



The trophic disorders that accompany affections of the vasomotor nerves are 

 deserving of especial consideration. Paralysis of the vasomotors gives rise, in 

 addition to vascular dilatation and local increase in the blood-pressure, also to 

 increased transudation from the capillaries. In consequence of the loss of the 

 muscular activity in the vessels the blood-stream becomes slowed, and stagnates; 

 as a result, the capillaries are dilated and the slowly moving blood in them becomes 

 markedly venous, so that the skin acquires a livid color. Further, normal trans- 

 piration is interfered with, so that dryness of the epidermis results, and often 

 also desquamation and fissuration. Passive hyperemia, a tendency to occlusion 

 of the capillaries and to the formation of thrombi in the veins, together with 

 passive transudates and edematous swelling, are not rare. Also the normal growth 

 of the hair and the nails is readily interfered with, the skin exhibits increased 

 vulnerability and the nutrition of all of the remaining tissues may suffer. In 

 consequence of long-continued irritation of vasomotor nerves the amount of 

 blood passing through the affected vessels becomes diminished, and it may be 

 conceived that, as a result, nutritive disturbances occur in the parts to be sup- 

 plied. Tangl found on long-continued faradic stimulation of the spinal cord a 

 reduction in oxidation-processes in the tissues, as a result of which gaseous inter- 

 change, and finally also the bodily temperature, fall markedly. 



In addition to the dominating vasomotor center in the medulla ob- 

 longata, the vessels are tinder the control of subordinate centers in the 

 gray matter of the spinal cord. This can be recognized from the following 

 observation : If the spinal cord be divided in an animal, all of the vessels 

 supplied by nerves arising below this level soon undergo paralytic dila- 

 tation, in consequence of section of the vasomotors from the medulla. 

 If the animal survive, the vessels regain their previous caliber in the 

 course of a few days, and the rhythmic movements of their muscular 

 coat are now controlled by the subordinate vasomotor centers in the 

 lower extremity of the spinal cord. 



The subordinate spinal centers can be stimulated directly through a dyspneic 

 state of the blood. Reflex stimulation also is possible; after destruction of the 

 medulla oblongata the arteries of the web of the frog's foot contract on irritation 

 of the sensory nerves of the opposite hind leg. In the dog a spinal vasomotor 

 center susceptible of reflex irritation is situated between the third and sixth 

 dorsal nerves (origin of the splanchnic), and a similar center is present in the 

 lower portion of the spinal cord. According to Spina the cerebral vessels have 

 such a center extending to the third cervical vertebra. 



If, after the section, the lower extremity of the spinal cord is crushed, 

 the vessels again undergo paralytic dilatation, in consequence of de- 

 struction of the subordinate centers. Even now, however, in surviving 

 animals the dilatation is gradually replaced by normal contraction and 

 rhythmic movement, and henceforth this movement of the vessel-wall 

 is controlled by the ganglia everywhere distributed throughout it. The 

 latter are thus capable of acting independently and of maintaining the 

 movement of the vessel-wall. Increased tension in the vessel causes 

 contraction of the muscular coat. Even the vessels of excised surviving 

 kidneys, through which blood is passed, exhibit these periodic fluctua- 

 tions in caliber. The observation is further worthy of mention that 

 the vessel-walls contract as soon as the state of the blood becomes in 

 marked degree venous. The vessels oppose a greater resistance to the 

 flow of venous blood than to that of arterial blood. Perhaps the general 

 disturbance of nutrition exhibited by individuals suffering from dyspneic 

 states of long standing is to be explained in this way. In any event the 



