50 



EXEECISE VII 



ANNOTATION 



Ohs. 27. Instances a purely spinal vaso- 

 motor reflex. Immediately after severance 

 of the cord from the brain such reflexes are 

 greatly depressed ('spinal shock'), and for 

 a considerable period. In the course of 

 days or weeks they recover, as is found in 

 cases of spinal transection in the cervical 

 region (Sherrington, Integrat. Act of the 

 Nervous Syst. p. 242). The depression may 

 be due to loss of some tonic support of the 

 spinal vasomotor centres from the great 

 vasomotor centre in the bulb. (Cf. F. H. 

 Pike, Am. Jnl. of Physiol, xxx. 436.) 



Ols. 28, 29. Of all individual efferent 

 nerves the splanchnic exerts the most 

 powerful vasoconstrictor effect as measured 

 by its influence on the general arterial 

 pressure. Starling speaks of it as ' the most 

 important vasomotor nerve in the body'. 

 This is because it contains vasoconstric- 

 tor nerve-fibres for so large a vascular 

 area, namely, that of the abdominal viscera. 

 It thus dominates directly and indirectly the 

 distribution of the blood for the time being 

 throughout the vascular system. Its vaso- 

 constrictive influence can therefore be studied 

 not only by direct inspection of the blanching 

 of the intestine, kidney, &c., but also, as 

 in the first part of this exercise, by observing 

 the rise of general arterial pressure which 

 its stimulation produces. De Cyon and 

 Ludwig discovered (1866) the vasoconstrictor 

 effect of stimulating the peripheral stump of 

 this nerve [JBer. d. Sachs. Gesellsch. d. 

 Wissensch., math.-phys. CI. p. 315). The 

 cardiac acceleration they did not notice. 



Johansson noted, 1891 {Arch. f. Physiol. 

 p. 103), that the rise of a. p. produced by 

 splanchnic-nerve stimulation occurs in two 

 steps. In the cat a distinct slight fall 

 commonly separates the steps, and T. E. 

 Elliott, investigating this, found, Jan. 1912, 



that the fall and second rise are caused by 

 secretion into the blood of adrenalin, thus 

 confirming the statement by K. P. Dreyer, 

 1889, based on other grounds (Amer. Jnl. 

 of Physiol, vol. ii, p. 203), that the splanchnic 

 nerve contains secretory fibres for the 

 adrenal medulla, which, as a ductless gland, 

 sheds its secretion directly into the blood. 

 Elliott's paper, Jnl. of Physiol, vol. xliv, 

 p. 396, should be read. The second rise of 

 a. p. exhibits concomitant acceleration of the 

 heart. Anrep in Starling 's laboratory proved, 

 Dec. 1912 [Jnl. of Physiol vol. xlviii, p. 307), 

 that this acceleration is due to the adrenal 

 secretion provoked by the splanchnic stimu- 

 lation, and that it persists after extirpation 

 of the accelerator nerves, i. e. by action of 

 the adrenalin (cf. your previous exerc. Ill, 

 § III) on the accelerator receptive sub- 

 stance (Langley) in the heart. Cf. also 

 Parsons and Swale Vincent, Trans. Roy. 

 Soc. Canada, xi. lUd. The relative degree 

 of acceleration of heart is great in pro- 

 portion as the beat-rate is slow prior to 

 the splanchnic stimulation, e.g. in your 

 experiment. 



Obs. 31. The remarkable heightening 

 of arterial pressure produced by intra- 

 venous injection of extract of the pitui- 

 tary body was discovered by Oliver and 

 Schafer in 1895 {Jnl. of Physiol, vol. xviii, 

 p. 276). Howell, in 1898, pointed out that 

 the effect is confined to extracts of the 

 posterior lobe {Jnl. of Experim. Med. vol. 

 iii, p. 215). The posterior lobe is made of 

 pars nervosa and pars intermedia. Herring 

 has shown (1914) that the effect is yielded 

 by extracts of either pars nervosa or pars 

 intermedia alone, but more strongly by the 

 former {Quart. Jnl. of Expl. Physiol, vol. 

 viii, p. 267). ' Infundin ' is the name given 

 to a commercial sterilized extract of the 



