of Edinburgh, Session 1867 - 68 . 
229 
Their reason for this selection is, that, as far as it is possible to 
judge from previously known facts, replacement does not produce 
nearly so great a change of physiological action as addition does. 
Thus, comparing the action of carbonic oxide and carbonic acid, 
hydrocyanic acid and methylamine, arsenious and kakodylic acids, 
strychnia and brucia, and the salts of the ammonium bases derived 
from them, it may be seen that addition, in many cases at least, 
diminishes or removes physiological activity. This comparison 
leads to a suspicion that physiogical activity is in some way con- 
nected with chemical condensation , by which term the authors mean 
susceptibility of addition, whether the addition takes place by the 
increase of the atomicity of an atom, or of a group of atoms. This 
suspicion receives some confirmation from the fact, that such of 
the stable combinations of pentatomic arsenic and antimony, as 
have been examined physiologically, are stated to be inert, while 
all the soluble compounds of triatom ic arsenic and antimony are 
active ; similarly, the aromatic bodies are, as a rule, more active 
than the corresponding fatty bodies. The occurrence, however, of 
such poisons as alcohol, oxalic acid, and corrosive sublimate among 
saturated substances, and of comparatively inert condensed com- 
pounds, such as benzoic acid and salicine, shows that condensation 
is not the only condition of physiological activity. 
The statements of Stahlscbmidt and Schroff, in reference to the 
action of the salts of methyl strychnia, induced the authors to turn 
their attention, in the first place, to the effect of the addition of 
