138 THE MECHANISM OF THE CIRCULATION, 



more, the hind-limbs, which were at first hotter and more Hushed with 

 blood, became eventually as cool or cooler than the fore-limbs. In 

 pathological cases, the same phenomenon is constantly observed to follow 

 on section of all the nerves. 



The tone of the great splanchnic area is completely restored some 

 eight days after section of all the splanchnic nerves. 



It has been suggested that the sympathetic ganglia are centres of 

 retiex vasomotor action. An experiment ([noted in favour of this view 

 is the following : If the first thoracic ganglion be entirely separated 

 from connection with the spinal cord, and the ganglionic end of one 

 branch of the annulus Vieussenii be stimulated, the vessels of the head 

 and neck contract. This and similar phenomena are perhaps not true 

 reflexes. The effect may be produced by the stimulus running up the 

 efferent fibres and thence down the collaterals of the same fibres. These 

 collaterals pass into several branches of the ganglionic system. 1 



To show the tonic influence of the peripheral ganglion cells, Dastre 

 and Morat bring forward this experiment. On section of the cervical 

 sympathetic nerve below the superior cervical ganglion, scarcely any 

 vaso-dilatation is to be seen in the mucous membrane of the mouth, 

 but on destruction of the ganglion the dilatation becomes unmistak- 

 able. 2 



In certain places rhythmic contractions and dilatations of arteries 

 can be observed, movements which are apparently independent of the 

 central nervous system, or of any change taking place in the general 

 vascular system. 3 This phenomenon can be witnessed in the central 

 artery of the ear or saphena artery of the rabbit (especially when the 

 animal is excited), and in the web or mesenteric arteries of the frog. 

 The contractions or dilatations may not affect the whole length of 

 an artery, but be localised to one or other part. Certain drugs, such as 

 chloroform and amyl nitrite, when applied locally, produce dilatation 

 of the blood vessels. These drugs act 011 the peripheral mechanism, 

 for if injected into a carotid artery they primarily excite the vaso- 

 constrictor centre ; when injected into a jugular vein they produce, on 

 the contrary, primary vaso-dilatation. According to Stefani, dyspnoeic 

 blood locally causes dilatation of the blood vessels, centrally it provokes 

 vaso -constriction. 4 



An extract of the medulla of the suprarenal gland exerts a most 

 powerful local vaso-constrictor effect. If one drop of a 1 per cent, 

 extract of the dried organ in normal saline be placed upon the mesentery 

 of a frog, the arterioles are constricted for thirty to sixty minutes, and to 

 such a degree that the onward flow of blood in the capillaries may 

 entirely cease, and be replaced by a back-eddy from the veins. The 

 same result is obtained after destruction of the spinal cord. Similarly, 

 after the conjunctiva of the rabbit's eye has been congested by the 

 application of acetic acid, the vessels may be again constricted by a drop 

 of suprarenal extract. 5 



Traube-Hering curves. In addition to the ordinary respiratory 



1 Langley and Anderson, Journ. PhysioL, Cambridge and London, 1894, vol. xvi. 

 "- Dastre and Morat, "Recherches exp^r. sur le systeme nerv. vaso-moteur," p. 326. 



3 Schiff, Arch. f. physiol. Heilk., Stuttgart, 1854, Bd. xiii. S. 525 ; Riegel, Arch. f. d. 

 yes. Physiol., Bonn, Bd. iv. S. 350 ; Klemensiewicz, Sitzungsb. d. k. Akad. d. Wisscnsch., 

 math.-naturw. CL, Wien, 1887, Bd. xcvi. Abth. 3, S. 71. 



4 Stefani, Arch. ital. de biol., Turin, 1894, vol. xxi. pp. 245-248. 



5 George Oliver, Proc. Physiol. Soc., March 1897. 



