ELECTROLYTES AND THEIR ACTION 217 



increase of surface energy, normally produced by the liberation of lactic acid, 

 cannot take place. 



If the blood vessels of the frog are perfused with Ringer's solution and a trace of adrenaline 

 added, a marked constriction is shown by a slowing of the rate of flow. According to 

 R. G. Pearce (with Asher, 1913, p. 274), if pure isotonic sodium chloride is used, adrenaline 

 causes dilatation of the vessels. It appears that calcium is necessary for the normal effect of 

 adrenaline on the sympathetic nerve-endings. In experiments of this kind caution is necessary 

 on account of the spontaneous rhythmical changes which are apt to occur in the frog's blood 

 vessels under saline perfusion, as I have described (1901, 1). In fact, I have been unable 

 to confirm Pearce's results. This apparent reversal of an excitation to an inhibition will 

 come up for discussion again in a later page. 



There are two particular phenomena of physiological interest which appear 

 to be colloidal aggregations. These are the coagulation of the blood and that of 

 milk by rennet. For both, the presence of calcium is required. In the former 

 case the fact was first definitely proved by Arthus et Pages (1890), although 

 the favouring action of calcium salts had been noticed previously and it had 

 been shown by Ringer and Sainsbury (1890) that barium and strontium had 

 the same effect, but in less degree. Arthus et Pages, also, showed that strontium 

 could replace calcium. 



The clotting of milk by rennet is due to the peculiar properties of the calcium 

 salt of caseinogen. Whether the salts with the other alkaline earths behave in 

 the same way does not appear to have been investigated. 



Magnesium. Meltzer and Auer (1905) describe how the subcutaneous 

 injection into a rabbit of 1'7 g. of magnesium sulphate per kilogram produces in 

 thirty to forty minutes deep anaesthesia and paralysis and (1908) how this effect is 

 removed in a few seconds by the intravenous injection of about 8 c.c. of 3 per cent, 

 calcium chloride. The same experimenters (1909) show that the application of a molar 

 solution of magnesium sulphate to the surface of the medulla oblongata causes, 

 within fifteen minutes, abolition of the functions of all the medullary centre?. 

 Meltzer (1913) points out the value of a preliminary dose of magnesium sulphate in 

 ether narcosis. If 0'6 g. of crystallised magnesium sulphate per kilogram of animal 

 is given intramuscularly to rabbits (or 0'8 g. to dogs) a very small effect is 

 produced ; but if ether be given, profound anaesthesia results from one-tenth 

 of the dose usually required for mild anaesthesia. 



Sodium. It was shown by Overtoil (1904) that frog's muscle immersed in 

 isotonic cane-sugar (7 per cent.) loses its excitability, and that restoration can be 

 brought about by a sodium salt or, in a less degree, by a lithium salt, but not by 

 salts of potassium or ammonium. 



Nerves behave in a similar way. 



Potassium. The action of potassium is, in the main, but not always, a 

 paralysing one, as seen in the case of the heart. At the same time, its presence is 

 necessary to control the opposite action of calcium. 



It is probable that the powerful physiological action of potassium may be connected with 

 the rapid rate of migration of its ions. If the table on page 177 be consulted, it will be seen 

 that these ions have a higher transport number than any other cation, with the exception of 

 hydrogen. This fact will enable them to play a prominent part in the phenomena connected 

 with the electric charge on surfaces. In the formation of a Helmholtz double layer, potassium 

 ions will outdistance other cations and, therefore, tend to be in excess in the positively charged 

 side of the layer. 



Howell (1906) showed that, in the absence of potassium salts, the vagus nerve 

 loses its power of inhibiting the beats of the heart, and the similarity between the 

 action of potassium and that of the vagus nerve suggested to him (1906, p. 291) 

 the hypothesis that the action of this nerve might depend on the setting free, in 

 some way, of potassium. Howell and Duke (1908) found that an increase of 

 potassium could be detected in a small amount of Ringer-Locke's solution which 

 had passed repeatedly through a mammalian heart under vagus inhibition. 



Hemmeter, however, (1913) was unable to find any difference in the potassium content of 

 the ash of normal and inhibited hearts, but this would scarcely be expected to be the case. In 

 the blood contained within the heart of the dog-fish, under both conditions, again no difference 

 was found, but the amount diffusing into the blood might easily be within the limits of the 

 experimental error of the method used, that of ordinary chemical analysis. Of more interest 



