ELECTROLYTES AND THEIR ACTION 215 



Enzyme Action. Many enzymes are inactive in the absence of electrolytes. 

 In some cases, this appears to be due to the facilitation, by salts, of adsorption 

 between enzymes and their respective substrates. 



Hwmolysin. It was shown by Gengou (1908) that the hsemolysin of the 

 serum of the eel is inactive without electrolytes. 



Secretion. It will be seen later that the excitatory action of extracts of the 

 duodenal mucous membrane in causing the pancreas to secrete is not shown in 

 the absence of electrolytes. 



Electrical Excitation. Since salts are always present in living tissues, it is 

 clear that the result of applying an electrical current must be the separation to 

 a greater or less extent of the ions of opposite sign at the two electrodes. The 

 exciting effect of the cathode and the inhibitory effect of the anode is, no doubt, 

 connected with this fact. The opposite action of H* and OH' ions is a familiar 

 fact and has been already referred to. 



Smooth Muscle. Hooker (1911) shows in experiments on perfusion of the 

 blood vessels of the frog with saline solutions, that calcium produces contraction 

 of the muscular coat, while potassium and sodium cause relaxation. Gaskell 

 (1880-82, pp. 55 and 56) had already shown that acids cause relaxation, and 

 alkalies cause contraction. 



Pigment Cells. The fish, Fundulus, contains in its skin yellow and black 

 pigment cells. It has been shown by Spaeth (1913) that potassium salts expand 

 the former, contract the latter. Sodium salts have an opposite effect on both. 

 By photographing the same cell, it is seen that the expansion and contraction 

 does not concern the cell as a whole, since the processes remain permanently of 

 the same form. The pigment granules migrate inside the processes to and from 

 the centre of the cell. 



We may pass on to some special actions of individual ions. 



Calcium. Although, in certain processes, calcium can be replaced by other 

 alkaline earths, there are others in which this is not so. Barium, for example, 

 is especially toxic to the animal organism. The property of calcium to favour 

 consolidation or stability in colloidal systems, in opposition to that of the alkali 

 metals, which tend towards liquefaction in some cases, is, no doubt, rightly 

 indicated by Hoeber (1911, p. 446) as being of great importance in the explanation 

 of the physiological action of calcium. Moreover, the same author points out 

 that the action of a bivalent ion is much less violent than that of a multivalent 

 ion and is much more easily reversible. 



We have already seen the necessity of calcium for the heart beat of the 

 vertebrate, and Lovatt Evans (1912, 2, p. 410) has shown that the same statement 

 applies to that of the snail. The latter, however, is able to stand a much higher 

 concentration than that of the frog, beating quite normally in 2 per cent, calcium 

 chloride. Barium is quite as toxic as to the vertebrate heart, one part in 20,000 

 causing a marked systolic condition. 



Locke showed (1894) that calcium is also necessary for the transference of the 

 excitatory process from nerve to muscle and Overton (1904) showed that it is 

 equally necessary for the transmission of the excitatory state through the synapse 

 of a nerve fibre with a nerve cell. According to Busquet and Pachon (1908) when 

 the action of the vagus nerve on the frog's heart has been stopped by perfusion 

 with pure sodium chloride solution, as shown by Howell (1906), addition of 

 calcium chloride in extremely small amount is sufficient to restore the inhibitory 

 action to the vagus nerve. 



Clark (1912, p. 12) has shown that digitoxin (the active substance of the 

 foxglove) is inactive without calcium. 



In Fig. 66 the heart of the frog is seen to be at first beating normally in Ringer's 

 solution. At A, calcium-free Ringer's solution is perfused to wash away calcium, and 

 at A', repeated circulation of the same 3 c.c. of the same solution is established. The feeble 

 beat seen in the tracing continues for hours under these conditions. At B, a trace of calcium 

 chloride is added ; the beat returns to normal. At B', O'Ol mg. of digitoxin is added and 

 at c, perfusion with calcium-free Ringer's solution is recommenced. It will be seen tJ 

 although the beat is somewhat stronger and slower, the typical systolic tone, which the drug 

 normally produces, is absent. At D, the normal amount of calcium chloride (0'02 per cent.) is 



