THE VASOMOTOR CENTER AND NERVES. 767 



Pfluger found that a rabbit with division of the cervical cord pro- 

 duced more carbon dioxid when the surrounding temperature was ele- 

 vated and less when the temperature was lowered. The human being 

 injured in a similar manner exhibits analogous conditions, being more 

 readily cooled when the surrounding temperature is low-and more readily 

 overheated when the surrounding temperature is high. 



Influence upon the Temperature of the Entire Body. Irritation or 

 paralysis of vasomotor nerves within small areas has practically no 

 influence upon the temperature of the entire body. If, however, the 

 vessels in an extensive area of the skin are suddenly dilated by paralysis 

 of their vasomotor nerves, the temperature of the entire body falls, be- 

 cause much more heat is given off from the dilated vessels than under 

 normal conditions. This is the case, for example, after high division of 

 the spinal cord. Inhalation of two or three drops of amyl nitrite is also 

 attended with reduction in the bodily temperature in man in consequence 

 of the resulting dilatation of the vessels of the skin. Under opposite 

 conditions of irritation of extensive areas the temperature of the body is 

 elevated because the constricted vessels give off less heat. This fact 

 explains in part febrile elevations in temperature. 



Also the cardiac activity, that is the number and the energy of the 

 contractions of the heart, is greatly influenced by the state of irritability 

 of the vasomotor nerves. If these nerves are paralyzed throughout 

 considerable areas, the vessels whose walls contain muscle-fibers dilate, 

 and the blood itself does not reach the heart with its usual rapidity and 

 abundance, as the pressure under which it flows has become considerably 

 essened. The consequence is that the heart makes extremely small, 

 slow and labored contractions, somewhat like a damaged pump, to which 

 sufficient material is not sent for propulsion onward. Strieker even 

 observed arrest of the heart in the dog on extirpation of the spinal cord 

 between the first cervical and the eighth dorsal vertebra. Conversely, 

 it is known that on irritation of the vasomotor nerves, in consequence of 

 the resulting contraction of the vessels with a muscular coat, the blood- 

 pressure rises considerably. As the arterial pressure is effective up to 

 the left ventricle, it causes, as a mechanical irritant to the wall of the 

 , heart, an increase in the activity of the heart, with respect both to the 

 number of beats and to their vigor, in the course of a short while. As 

 a result, the circulation, already accelerated by the increase in pressure 

 in the arterial system in consequence of the arterial contraction, is further 

 accelerated. 



By far the most extensive area of the circulation is controlled by the splanchnic 

 nerve, as it innervates the large branches of all of the arteries of the abdomen. 

 Irritation of this nerve is, therefore, followed by marked increase in the blood- 

 pressure. Conversely, paralysis of the nerve is attended with such marked stag- 

 nation of blood in the dilated abdominal vessels that all the remaining portions 

 of the body become anemic, and death may even result, in a measure in conse- 

 quence of intravascular hemorrhage. For the same reason animals die of anemia 

 after ligation of the portal vein. 



The capacity of the interior of the vascular system, by reason of its dependence 

 upon the vasomotor nerves, has obviously also an influence upon the bodily weight, 

 especially in consequence of variations in the amount of fluid taken up into or 

 given off from the blood. Strong irritation of the vasomotor apparatus may cause 

 a fall in bodily weight through rapid loss of water. In this category belongs 

 probably the loss of weight observed by some after epileptic convulsions, in 

 consequence of polyuria, increased sweating, secretion of tears or of saliva. Con- 

 versely, paralysis or paresis of the vasomotor nerves causes dilatation of the 



