ON THE PHYSIOLOGICAL ACTION OF MEDICINES. 85 
has not been experimented with. The salts of soda and silver also agree in 
the effects they produce, although presenting a more striking contrast in many 
of their chemical properties than is to be found in any other class. On the 
other hand, potash and ammonia, two substances between which well-marked 
isomorphous relations exist, differ to a certain extent in the phenomena they 
give rise to when introduced into the blood. It is possible that the compound 
nature of the radical of ammonia, differing so completely as it does from the 
other inorganic radicals, may introduce certain modifications in its relation 
to organized compounds. The only other fact that my investigations have 
made me acquainted with, which appears to oppose itself to this law, is, the 
analogy that exists to a certain extent between the salts of lead and the 
chlorine group and silver. As regards the more marked phenomena pro- 
duced by the salts of lead, they are such as its connection with strontian and 
baryta would lead us to suppose ; but in one respect, viz. in their action on 
the lungs, they resemble the salts of silver. As regards this anomaly I would 
merely observe, that galena and sulphuret of silver are found under the same 
form. 
Such is the evidence with which my researches have furnished me, in sup- 
port of the law of the analogous action of isomorphous substances on 
organized beings, and I think it sufficient to justify us in admitting that the 
molecular reactions that take place between the elements of living bodies 
and inorganic substances are to a great extent independent of chemical affi- 
nity, but are connected with those properties of matter which are expressed 
by its isomorphous relations. It is evident that this law must lead to important 
modifications in the investigation of physiological phenomena: in considering 
the action of unorganized substances on organized beings, it is clear that 
our attention must not be so exclusively directed to the chemical properties 
of these substances: it must not be as alkalies or acids or salts that their 
action on organized beings must be investigated, but as regards their isomor- 
phous relations, or those properties of matter which are evidently connected 
with the form it assumes, and which have recently been elucidated by the 
researches of Kopff. But whilst this lay would tend to remove the inves-_ 
tigation of physiclogical phenomena from the domain of pure chemistry, it is 
far from leading us to conclude that the reactions that take place amongst 
materials of which organized beings are composed are essentially of a different 
character from those which we observe amongst the simpler forms of matter. 
The difference between the more simple combinations of the elements with 
One another and those they form with the more complicated compounds of 
carbon, hydrogen, oxygen and nitrogen that exist in the living body, seems 
' to be, that in the former instance they combine under the influence of che- 
mical affinity, whilst in the latter it would appear to be a physical polarity 
that influences the formation of the compound:: it is the former power that 
gives rise to the union of sulphuric acid and soda, whilst the latter causes 
the compound to assume a definite crystalline form. It would appear, in fact, 
as if the force of chemical affinity was more or less neutralized in living 
__ beings, and that their elements are held together by other forces than those 
_ which prevail amongst unorganized compounds. In the present early stage 
__ of these researches, I would not attempt to generalize this law beyond that 
j velass of facts to which it has been proved experimentally to apply ; it may 
admit of a far more extended application, embracing in its expression not 
merely the combinations of the compound elements of organized beings, but 
also the combinations of carbon, hydrogen, nitrogen and oxygen, of which 
_ these elements consist. In the present imperfect state of our knowledge, it 
uld be hazardous to offer an opinion on the nature of the compounds 
