84 REPORT—1845. 
If the dose be larger (25 grains of iodic acid for instance), the passage of the 
blood through the lungs becomes at once arrested, and the animal rapidly 
dies from congestion of the venous system. After death the lungs are found 
congested and red, serous effusion having taken place in their tissue as well 
as in the air-passages. The heart generally contains a medium quantity of 
dark blood, which coagulates firmly. If the thorax is opened immediately 
after death, the ventricles are found beating rhythmically, although the auri- 
cles have lost all trace of irritability,—a fact which forms a curious exception 
to the general rule, and which has only been observed in connection with 
this class of substances. When injected into the arteries, the phenomena 
produced by iodic acid are very extraordinary. The first effect that followed 
the introduction of six grains of the acid into the artery was an immediate 
diminution of the pressure in the arterial system: in the instance alluded to, 
it fell in the course of a few seconds from six to eight inches down to two, 
the heart’s action being very slow ; the animal cried, respiration became sus- 
pended, and in about a minute it lay to all appearance quite dead ; after an- 
other minute however the pressure in the arterial system suddenly increased to 
nine inches, the heart beating quite regularly, although the animal still lay as 
if dead; the pressure gradually diminished, and at four minutes after the in- 
jection, and three minutes after every external sign of life had ceased, it had 
again sunk to five inches. A most curious phenomenon now presented itself, 
viz. a sudden rise of full three inches, in the pressure of the blood in the 
arterial system. This increase in the pressure was followed by two respira- 
tory movements, and by slight motion in the legs and tail. After this the 
pressure gradually sunk, and the heart stopped seven minutes after the injec- 
tion. The chloric and bromic acids give rise when injected into the arteries 
to phenomena exactly analogous to those just described: with hydrochloric 
acid the action of the heart does not continue so long after respiration has 
ceased, nor has the augmentation in the pressure after the cessation of re- 
spiratory movements been observed with this substance; this might possibly 
be owing to its not containing oxygen. 
Having now brought forward the facts which have been ascertained since 
my last report, in support of the analogous action of isomorphous substances 
on animals, I propose to take a general review of the whole of the evidence 
we are now in possession of relating to this law, and also of those facts which 
appear to militate against it; merely premising, that, in the present imperfect 
state of our knowledge as regards the isomorphous relations of bodies, it is 
not to be expected that a first attempt to arrive at any generalization found- 
ed on these properties should not present many anomalies and apparent 
contradictions, which it will require further investigations to clear up, or 
which may lead to important modifications in the expression of the law itself. 
The evidence in favour of the law is derived from the following facts :—first, 
the similarity of action of the following isomorphous substances belonging 
to the magnesian class; viz. magnesia, lime, manganese, iron, cobalt, nickel, 
zine, cadmium, copper and bismuth,—substances which present striking differ- 
ences in their ordinary chemical affinities, but which agree in being isomor- 
phous, and also in producing analogous phenomena on animals when intro- 
duced directly into the blood. The salts also of another well-marked isomor- 
phous group, viz. lead, strontia and baryta, closely agree in their actions on 
the animal system. Palladium and platinum, in the effects they produce 
when introduced directly into the blood, lend their support to this law. 
Phosphorus, antimony and arsenic, a strictly isomorphous group, give rise to 
analogous reactions on the animal economy. ‘The chlorine group also fully 
bears out the law, at least as regards iodine, bromine and chlorine, for fluorine 
