THE VASOMOTOR CENTER AND NERVES. 769 



vessel-walls, however, appear after the series of procedures described 

 not to attain again the complete mobility and reactivity that they pos- 

 sess under normal conditions. 



Through the intermediation of these peripheral vessel-ganglia the movements 

 of the vessels also appear to take place that are observed to occur on application 

 of direct mechanical, chemical or electrical irritation to the vessels. The arteries 

 contract often to the point of obliteration of their lumen. Amyl nitrite and 

 digitalis have an effect upon the lumen. The pulsating veins in the bat's wing 

 continue their movement after division of all of the nerves, and this is indica- 

 tive of the local innervation through peripheral nerve-centers. 



Finally, the cerebrum undoubtedly has an influence upon the vaso- 

 motor center, as is shown by the sudden pallor of the external integument 

 in conjunction with emotional disturbances, such as fright, fear. This 

 observation has received a satisfactory explanation in the discovery 

 made by Eulenburg and Landois that the gray cortex of the cerebrum 

 contains a circumscribed area (in the cruciate sulcus in the dog), irri- 

 tation of which gives rise to reduction of temperature and destruction 

 to elevation of temperature in the contralateral extremities. From this 

 area fibers therefore probably pass to the center in the medulla, which 

 they stimulate to either increased or diminished activity. In this way 

 is to be explained the fact, as observed by Landois together with Budge, 

 that irritation of both cerebral peduncles causes contraction of all of the 

 vessels. Heidenhain noted, accordingly, that irritation in the further 

 course, at the junction between the pons and the medulla oblongata, 

 caused rapid rise in the bodily temperature. 



Emotional influences generally increase the tone of the vessels (as observed 

 in the arm), while fatigue and joy diminish it. 



Although the medulla contains a dominating vasomotor center for 

 all of the vessels in common, it is to be assumed that this is divisible 

 into a number of central points lying close together and controlling 

 definite vascular areas. In this connection there have been isolated 

 the centers for the vessels of the liver and for those of the kidneys. 



Finally, it should be mentioned that certain poisons especially stimulate the 

 vasomotor apparatus, such as ergotin, tannic acid, balsam of copaiba and cubebs; 

 while others at first stimulate and then paralyze, such as chloral hydrate, morphin, 

 laudanosin, digitalin, veratrin, physostigma. alcohol; while still others rapidly 

 paralyze, such as amyl nitrite, carbon monoxid, atropin and muscarin. The 

 paralyzant action of poisons is recognized from the fact that after division or 

 paralysis of the cardiac fibers of the vagus and of the accelerator nerve irritation 

 of either the pressor or the depressor nerves is unattended with any effect. Cer- 

 tain agents having a pathological effect have an influence upon the vasomotor 

 nerves. In surviving organs, narcotics and antipyretics cause dilatation and 

 members of the digitalis-group contraction. 



The veins are controlled by vasomotor nerves, for example, the ear- 

 veins of the rabbit through the cervical sympathetic, the portal vein 

 through the splanchnic, the veins of the hind leg through the sciatic. 

 On the whole, the venomotors pursue the same course as the arterio- 

 motors and the sweat-fibers. 



Little is known with regard to the dependence of the lymphatics upon 

 the nerves. Camus and Gley observed on irritation of the peripheral 

 extremity of the splanchnic nerve that the receptacle for the chyle gener- 

 ally dilated. Irritation of other sympathetic fibers caused contraction 



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