676 LOCAL AND SECONDARY RESULTS OF VASO-MOTOR ACTION. 



becomes cooler than the ear on the sound one. If in man the motor muscular nerves, as well 

 aTX YaTmotor fibres, are paralysed, then the paralysed limb becomes cooler because the 

 mrXsed muscles no longer contract to aid in the production of heat ( 338), and also because 

 the dilatation of the muscular arteries, which accompanies a muscular contraction, is absent. 

 Should atrophy of the paralysed muscles set in, the blood-vessels also become smaller. Hence, 

 paralysed HiiiUs in man generally become cooler as time goes on. The primary effect, however, 

 in a fimb, eg., after section of the sciatic or lesion of the brachial plexus, is an increase of the 

 terapem tun.-. ' - 



If at the same time, the vaso-motor nerves of a large area of the skin be 

 paralysed, e.g. t the lower half of the body after section of the spinal cord, then so 

 much heat is given off from the dilated blood-vessels that, either the warming of the 

 skin lasts for a very short time and to a slight degree, or there may be cooling 

 at once. Some observers (Tschetschichin, Naunyn, Quincke) observed a rise of the 

 temperature after section of the cervical spinal cord, but Riegel did not observe this 

 increase. 



2. Effect on the Temperature of the Body. Stimulation or paralysis of 

 the vaso-motor nerves of a small area has practically no effect on the general 

 temperature of the body. If, however, the vaso-motor nerves of a considerable area 

 of the skin be suddenly paralysed, then the temperature of the entire body falls, 

 because more heat is given off from the dilated vessels than under normal circum- 

 stances. This occurs when the spinal cord is divided high up in the neck. The 

 inhalation of a few drops of amyl nitrite, which dilates the blood-vessels of the 

 skin, causes a fall of the temperature (Sassetzki and Manasse'in). Conversely, 

 stimulation of the vaso-motor nerves of a large area increases the temperature, 

 because the constricted vessels give off less heat. The temperature in fever may 

 be partly explained in this way ( 220, 4). 



The activity of the heart, i.e., the number and energy of the cardiac con- 

 tractions, is influenced by the condition of the vaso-motor nerves. When a large 

 vaso-motor area is paralysed, the blood-channels are dilated, so that the blood does 

 not flow to the heart at the usual rate and in the usual amount, as the pressure is 

 considerably diminished. Hence, the heart executes extremely small and feeble 

 contractions. Strieker observed that the heart of a dog ceased to beat on extirpat- 

 ing the spinal cord from the 1st cervical to the 8th dorsal vertebra. Conversely, 

 we know that stimulation of a large vaso-motor area, by constricting the blood- 

 vessels, raises the arterial blood-pressure considerably. As the arterial pressure 

 affects the pressure within the left ventricle, it may act as a mechanical stimulus 

 to the cardiac wall, and increase the cardiac contractions both in number and 

 strength. Hence, the circulation is accelerated (Heiden/iain, Slavjansky). 



Splanchnic. By far the largest vaso-motor area in the body is that controlled by the 

 splanchnic nerves, as they supply the blood-vessels of the abdomen ( 161) ; hence, stimulation 

 of their peripheral ends is followed by a great rise of the blood-pressure. When they are 

 divided, there is such a fall of the blood-pressure that other parts of the body become more 

 or less anaemic, and the animal may even die from " being bled into its own belly," i.e., from 

 what has been called "intravascular haemorrhage. " Animals whose portal vein is ligatured 

 die for the same reason (C. Ludwig and Thiry) [see 87]. The capacity of the vascular system, 

 depending as it does in part upon the condition of the vaso-motor nerves, influences the body- 

 toeight. Stimulation of certain vascular areas may cause the rapid excretion of water, and we 

 may thus account in part for the diminution of the body-weight, which has been sometimes 

 observed after an epileptic attack terminating with polyuria. 



Trophic disturbances sometimes occur after affections of the vaso-motor nerves ( 342, I., c). 

 Paralysis of the vaso-motor nerves not only causes dilatation of the blood-vessels and local 

 increase of the blood-pressure, but it may also cause increased transudation through the capil- 

 laries [ 203]. When the active contraction of the muscles is abolished, the blood-stream at 

 the same time becomes slower, and in some cases, the skin becomes livid, owing to the venous 

 cougestion. There is a diminution of the normal transpiration, and the epidermis may be dry 

 and peel off in scales. The growth of the hair and nails may be affected by the congestion of 

 blood, and other tissues may also suffer. 



Vaso motor Centres in the Spinal Cord. Besides the dominating centre 



