196 J. Blake—Connection between Isomorphism, ete. 
in the same isomorphous group generally increases with the 
atomic weight. For instance, in the first group, the relative 
physiological activity between the compounds of Li and K is 
125:1; in the 2d group, between Mg and Cd 104: 1; in the 
3d group, between Be and Fe 3:1; in the 4th group, between 
Ca and Bal0:1. In the 5th group, the quantities used were 
. so small, and in the case of Pt and Ir double salts had to be 
in their action from the other bodies in the soda group. Iam 
aware that the isomorphism of soda and potash has been called 
in question by some chemists, and it certainly does not fit into 
the soda group, by the relative increase of its specific weight 
with its atomic weight. As regards the salts of ammonia, they 
are also totally distinct in their action from the salts of the 
soda group, resembling to a certain extent many of the organic » 
poisons by their action on the nervous system. The salts of 
silver and of lead also differ in some respects in their physio- 
logical action from the other substances of the group to whic 
they belong. They both give rise to the well marked reactions 
characterizing each group, yet they both produce certain 
effects on the capillary circulation in which they resemble each 
other, but in which they differ from other members of the 
group in which each is placed. Czesium also differs from the 
other members of the first group by its action on the nervous sys- 
tem.* With these exceptions the substances contained in the 
same group agree with each other, in the effects they produce on 
the pulmonary and systemic circulation in their action on the 
eart, and on the nervous and muscular systems, and in the 
physical changes they give rise to in the blood. In the present 
imperfect state of our knowledge as regards the isomorphous 
relations of the elements, it would be useless to speculate on 
the nature of the changes induced on living matter by dif- 
ferent groups of isomorphous substances. se 
~ changes must be quite different from those occurring 
in ordinary chemical reactions, as in these reactions the greater 
* It will be seen on referring to the table that these three substances present 
the most striking anomalies as to the connection of physiological intensity with 
increased atomic weight. 
