319 
to name electrogen, must be admitted into the list of supposed 
elements: that it was not a union of an electrolytic compound 
whose action was unknown ; and that probably it exists in coms 
bination in various forms of matter, which at present are consid- 
ered elementary, but which in reality are not so. 
A paper on manures considered as stimulants to Cnyletadions 
was communicated by Dr. Daubeny. The author discusses the 
question as to the sense in which manures can be considered to 
act as stimulants to plants. It is evident that if the term stim- 
ulus be understood in an acceptation similar to that in which 
it is employed with reference to the animal economy, it ought to 
be confined to bodies, which by their presence, assist in promot- 
ing the secretion and assimilation of the nutritious materials pres- 
ent, and ought not to include such as themselves afford materials 
for secretion. 'Thus salt and other condiments do not themselves 
nourish the animal; but by their presence, induce its secreting 
surfaces to assitnilate more readily the substances presented to 
them. Now, it becomes a fit subject for inquiry, whether ma- 
hures operate in the former manner or in the latter; and likewise 
whether the fact, that certain of them act less beneficially at sub- 
sequent periods of their application than they did at first, admits 
of being explained om the recognized principle that “ stimuli lose 
their full effect upon living matter when frequently repeated.” 
Dr. D. adduced several facts which led to the inference that the 
nitrates of soda and of potassa operate favorably upon certain 
crops by communicating to them nitrogen; and the reason why 
these salts sometimes have appeared to leave the land in a worse 
condition than before their use, is not owing to their being stim- 
uli, and therefore amenable to the law above quoted ; but is be- 
cause the free supply of nitrogen afforded by the decomposition 
of the nitrates, had caused the plant to absorb a larger portion of 
those other ingredients, such as phosphate of lime, silicate of po- 
tassa, &c., which are present only in a limited quantity in the 
soil, thus tending to exhaust it of these materials, and causing 
thereby an inferior crop to be produced on the following -year. 
Now, though it may be true that the nitrates in this manner in- 
directly stimulate the vital energies of the plant, yet it was con- 
ceived that the term stimulus had better be abandoned with ref- 
erence to such cases, as its adoption might lead to an erroneous 
impression in the mind of the farmer with respect to the proper 
