HORMONES, DRUGS, AND TOXINS 711 



It is an intensely active substance. Pysemsky and Kravkov (1912), in 

 perfusing the ear of the rabbit with Ringer's solution, to which adrenaline was 

 added, found that one part in two hundred and fifty millions of the saline 

 solution could be detected. 



The cells which secrete adrenaline, that is, those of the medulla of the glands, 

 stain a brownish-yellow colour with potassium bichromate ; hence the name given 

 to them of " Chroniaffine " tissue. Similar cells are found throughout the 

 vertebrate kingdom in various situations. In the lamprey the system is arranged 

 segmentally. The reaction is also given by certain nerve cells in invertebrates, 

 and J. F. Gaskell (1914) points out that the presence of such cells is correlated 

 with the development of a contractile vascular system. In the leech, each 

 segmental ganglion contains six chromaffine nerve cells, and the contractile 

 vascular system consists of a series of segmental units, each under the control 

 of a segmental ganglion. The chromaffine cells contain a substance similar to 

 adrenaline, and the contractile vessels react to adrenaline as those of the 

 vertebrate do. There appears then to be some close connection between these 

 chromaffine nerve cells and those of the medulla of the suprarenal bodies ; more- 

 over, the relation between the action of adrenaline and the sympathetic system, 

 already spoken of, shows a further connection. J. F. Gaskell suggests that the 

 chromaffine nerve cells of the invertebrate are the common ancestors of the 

 adrenaline-secreting chromaffine system and the sympathetic nervous system of 

 the vertebrate. Thus we find the contractile vascular system regulated both by 

 the sympathetic nerves and by secretion of adrenaline. 



Further evidence is found in the mode of development of the medulla of the 

 suprarenals. As Balfour showed (1878, pp. 242-245), this has the same origin as 

 the sympathetic system, and Kohn (1902) showed that the development of these 

 cells of the medulla is from a series of groups of cells in connection with the 

 sympathetic along the body axis. Rudiments remain for some years in scattered 

 situations, as along the aorta and to form the carotid gland, but the main mass 

 becomes the suprarenal ganglion, or medulla of the suprarenal body. The 

 scattered remains are called paraganglia. 



We have seen that one of the characteristics of the sympathetic outflow is the 

 connection of each fibre with a cell before passing on to its destination. Now 

 Elliott (1913, 2) has shown that the supply to the adult suprarenal gland has no 

 cell station previous to the cells of the medulla themselves, a further fact in 

 evidence of the similarity of these cells to those of the sympathetic ganglia. 

 Elliott (1913, 1) points out that there are two types of cells to which the 

 sympathetic fibres from the spinal cord pass : 



(1) The sympathetic ganglion cell, which is distally united to the plain muscle 

 cell by its axone process, and so provides a path for the nervous impulse. 



(2) The medullary or paraganglion cell, which is not in connection with the 

 muscle, but is equally innervated from the spinal cord, and secretes a chemical 

 substance into the blood, which can produce an identical stimulation of the muscle 

 through its myo-neural junction. 



These may have been originally identical, and the liberation of adrenaline an 

 essential part of the nerve impulse. But, at the present time, the paraganglion 

 cell secretes adrenaline, which maintains the smooth muscle in a state of ex- 

 citability, ready to react to the nerve impulses from the sympathetic fibres. 

 Elliott's general scheme is reproduced in Fig. 252. 



Fascinating as this scheme is, there are some minor points which are not 

 completely cleared up. The sweat glands, although innervated by the sympathetic, 

 are not excited by adrenaline. Further, we have seen that the presence of the 

 suprarenal bodies is not necessary for the production of vascular constriction. It 

 may well be, however, in this latter case, that the loss of excitability does not take 

 place rapidly. 



Elliott (1912) has shown that the various states associated with stimulation of 

 the splanchnic nerves cause discharge of adrenaline into the blood, causing rise of 

 blood pressure, and the other results of sympathetic stimulation. Such states are 

 fright, anaesthesia, stimulation of afferent nerves, and so on. Reference to the 



