950 7. MERCURIALS 



potential (Brady et al., 1958), which may indicate that the mercurial must 

 act on the external surface of the membrane to block conduction. The 

 changes in the structure of the myelin sheath of nerves brought about by 

 Hg++ at high concentrations (around 10 mM) are certainly not relevant to 

 acute experiments with low concentrations, but in chronic mercury poison- 

 ing it is possible that sufficient Hg++ is incorporated in the myelin to disturb 

 nerve function (Millington and Finean, 1958, 1961). Thus at the present 

 time we cannot decide whether the primary action of the mercurials is on the 

 axon or on the synaptic regions, or on both, especially in chronic poisoning. 



Skin 



Various types of skin reaction to the mercurials administered both sys- 

 temically and topically have been recognized for years. Some of these are 

 undoubtedly of the allergic or sensitivity category and need not concern us. 

 Mercurial diuretics, like mersalyl, when injected in small amounts into the 

 skin cause blisters, and Hahn and Taeger (1931) concluded that there is a 

 relationship between diuretic activity and vesication. Almkvist (1922) had 

 claimed that mercurials cause vascular dilatation in the skin, with result- 

 ing edema, by a paralysis of the sympathetic nerves, but there is little evi- 

 dence that this is a significant factor. Hellerman and Newman (1932) noted 

 that alkyl mercurials are powerful vesicants and can cause a severe der- 

 matitis. These early observations are of interest in the light of the relation- 

 ship between SH group reaction in the skin and vesication established by 

 work on the arsenical war gases, and one might postulate that the mercur- 

 ials have a metabolic basis for their effects on skin, perhaps an inhibition 

 of the cycle. Hg++ reduces frog skin potentials across both borders and in- 

 creases the outer membrane resistance (Lodin et al., 1963). 



EFFECTS OBSERVED IN THE WHOLE ANIMAL 



It is difficult to present the toxicology of the mercurials concisely be- 

 cause the effects depend on the type of mercurial, the species considered, 

 whether the poisoning is acute or chromic, the route by which the mercurial 

 is taken into the body, and many other factors. The symptoms of chronic 

 mercury poisoning (mercurialism) in man are quite variable and usually 

 not correlated with the blood or urinary levels of mercury. Frequently 

 urinary mercury may be considerably higher than the normal range and 

 yet no symptoms occur; however, definite symptoms may sometimes be ob- 

 served in those whose level is in the normal range. This lack of correlation 

 with urinary levels and the protean nature of the poisoning not only make 

 diagnosis frequently difficult but indicate that the individual pattern of 

 response must relate to a number of obscure factors, such as hereditary 



