328 OF THE CIRCULATION OF THE BLOOD. 



of the sympathetic contains the vaso-motor nerves of the skin of the head, 

 the conjunctiva, and salivary glands. The splanchnics, which are exceed- 

 ingly important vaso-motor nerves, supply the very dilatable vessels of the 

 abdominal viscera. The vaso-motor nerves for the upper extremities pass 

 from the roots of the middle dorsal nerve to the sympathetic cord, and thus 

 reach the first dorsal ganglion, from whence they pass into the brachial 

 plexus (E. Cyon). Those for the lower extremities proceed from the rami 

 commuuicautes of the sympathetic into the anterior roots of the spinal 

 nerves. 1 The vaso-motor centre is capable of being excited and of being 

 depressed. In the former case the smaller arteries either of a definite region 

 or of the whole body contract, and the blood-pressure rises. In the latter 

 case the smaller arteries of a territory of variable extent dilate or relax and 

 the blood-pressure falls. This is usually accompanied by the accumulation 

 of blood in the veins of the abdominal viscera. The excitation of the centre 

 indicated by exaltation of the blood-pressure in the arteries can be effected 

 by the circulation through its vessels of blood charged with carbonic acid or 

 deficient in oxygen, and in a reflex manner by the irritation of almost any 

 of the sensory nerves, as those of the skin, 2 peritoneal layer of the stomach, 3 

 dura mater, 4 olfactory or nasal nerves 5 (providing the brain is uninjured, 

 Cyoii) ; also by irritation of the cervical sympathetic nerve, 6 and by certain 

 poisons, amongst which digitalis may be particularly mentioned. 7 [Some 

 poisons like thebain have the property of exciting the vaso-motor centre to 

 increased activity, but unlike strychnia thebain does not act on the vaso- 

 motor centres situated in the spinal cord.] 8 The vaso-motor centre can be 

 depressed, or its action inhibited, by irritation of the depressor nerve of the 

 vagus, and fibres having a similar depressing action run in the vagus below 

 the origin of the nervous depressor from the vagus. The term " Traube's 

 curves" is applied to the rhythmical variations of arterial pressure which 

 were observed by Traube w to occur in animals under the influence of Woorara 

 during the gradual rise of pressure that arises after complete cessation of the 

 respiratory movements and section of both vagi. Kowalewsky and Adamu'k 

 and Hering have shown that the rise and fall of pressure constituting Traube's 

 curves are independent alike of variations in the heart's action, of blood- 

 pressure, and of asphyxia, and that they are referable to the circulation of 

 nou-arterialized blood through the respiratory centres, and to variations in 



1 The nerves of the vessels supplying a muscle do not always accompany the motor 

 trunks of that muscle. Thus the biceps femoris receives its motor nerves from the 

 sacral plexus, but its vaso-motor nerves come from the lumbar plexus through the 

 crural nerve. 



2 Loven. 



3 Mayer and Pribrum, Sitz.-ber. d. Wion. Akad., Bd. Ixvi, 1872. 



4 Ludwig and Dittmar, Lud wig's Arbeiten, 1870, p. 4. 



5 Hering and Kratschmer; Rutherford, Journal of Anat. and Phys., 1873, vol. vii, 

 p. 283; Brown-Sequard, Archiv. of .Scientific Med., 1873, p. 90. 



6 Aubert and Rocven, Kritische Untersueh., etc. Rostock, 1869. 



7 Brunton and Mayer, Journ. of Anat and Phys., Nov. 1872. Callenfels (Zeits. 

 f. Rat. Med., 1855, Bd. vii, p. 191) has noticed contractions of vessels of one car of a 

 rabbit occur when the opposite ear was pinched ; and Brown-Sequard (Journ de hi 

 Physiol , 1858, p. 504) observed that on immersion of one hand in cold water, the 

 temperature of the other uniformly fell, in one instance as much as 21 F. : a re>ult 

 which may perhaps serve to explain the effects of the application of cold in controlling 

 haemorrhage when applied to some distant part of the body. 



8 [I. Ott, Physiology, Act. of Thebain, Boston Med. and Surg. Journal.] 



9 Allgemein. Med. Centralzeitung, Nos 9,30,89,99, and Centralblatt, 185, p. 881. 

 See also Thiry, Sitz.-ber. d. Wien. Akacl., 18(54, p 32; Kowalewsky and Adamiik, 

 (Yntralbhitt, 1*118, p. 545; Hering, Sitz.-ber. d. k. Akad. YM Wien., Bd. Ix, 18(59 ; 

 Sanderson, in Handbook to Phys. Lab., p. 317, 1873. 



